Battery pack having a processor controlled battery operating system

ABSTRACT

A battery pack and a method of operating a battery system. The battery pack includes a rechargeable battery and a processor for monitoring the battery during charging and discharging. The processor receives data values representing the battery voltage, temperature and current, and the processor performs a series of calculations using those data values. The processor is part of a hybrid integrated circuit, which also incluses an analog-to-digital converter, a ROM and a RAM. Preferably, the integrated circuit comprises a multitude of layers, upper layers of the circuit form the ROM, and lower layers of the circuit form the RAM.

CROSS-REFERENCE

This application is a division of application Ser. No. 08/473,339 filedJun. 7, 1995 now U.S. Pat No. 5,710,501 which application is a divisionof application Ser. No. 08/336,945 filed Nov. 10, 1994, now U.S. Pat.No. 5,633,573.

FIELD OF THE INVENTION

The present invention relates generally to the art of rechargeablebatteries and more specifically to a smart battery for use in anintelligent device having power management capabilities. The inventionis a smart battery apparatus for controlling the operation ofrechargeable Nickel Metal Hydride (NiMH) or Nickel Cadmium (NiCad)batteries, and the like, to enable the reporting of accurate informationto the intelligent device for power management and charge controlspecific to the battery's state of charge and chemistry.

DESCRIPTION OF THE PRIOR ART

The advent of intelligent portable electronic devices such as notebookcomputers, video cameras, and cellular phones has enabled thedevelopment of smart rechargeable batteries that can communicate withthe intelligent device to provide accurate information on the battery'spresent state of charge, and how best to recharge the battery tomaintain maximum battery life, thus enabling the highest number ofcharge-discharge cycles. A user of such intelligent portable devicesutilizing such smart batteries will not only know how much charge isleft in the battery, but battery run time at various rates of powerconsumption. This enables the user to select a mode of operation thatwill enable maximum service life on the remaining state of charge and,how long the device will continue to operate.

Prior art rechargeable battery units have been provided with means forgenerating some desired information to their users, including forinstance, a charge monitor and fuel gauge such as that disclosed in U.S.Pat. No. 5,315,228 which discloses a method for calculating state ofcharge and reporting run time to empty to the host computer system.

However, there is a need for a rechargeable power unit that willaccurately maintain its own state of charge information even whennominally fully discharged such that a user will have instantaneousaccess thereof. Moreover, there is also a need for an intelligentrechargeable battery that can provide the user with an accurateprediction of its remaining operating time at various levels of powerconsumption. The user of such an intelligent device, such as a portablecomputer, can thus elect to power down a hard disk drive to extend theoperation of the portable computer for a longer period of time thanwould have been possible at the higher rate of power consumption.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a smartbattery device for use with a rechargeable battery to be installed in ahost computer that will optimize the performance of the rechargeablebattery throughout its life cycle.

It is another object of the instant invention to provide a smart batterydevice that includes a microprocessor for controlling a rechargeablebattery that performs battery capacity calculations for communication toa host computer device or a smart battery charge device.

It is still another object of the instant invention to provide a smartbattery device that includes a microprocessor for controlling arechargeable battery and that provides intelligence in the form ofpresent state of charge and battery charge parameters to a host devicefor communication to a smart charger.

It is yet still a further object of the instant invention to provide asmart battery device that includes a microprocessor for controlling arechargeable battery that monitors battery operating parameters such asvoltage, current, and temperature to thereby enable either a rapidcharging rate or an optimal charging rate from any charged state.

Still yet another object of the instant invention is to provide a smartbattery device that includes a microprocessor for controlling arechargeable battery that calculates predictive data such as thebattery's remaining life at the current rate of drain and at alternaterates of drain.

It is still a further object of the instant invention to provide a smartbattery device that is an application specific integrated circuit (ASIC)having analog and digital components.

Furthermore, another object of the present invention is to provide asmart battery device that includes an analog to digital (A/D) converterfor measuring battery charge parameters such as voltage, current, andtemperature.

Yet still another object of the present invention is to provide a smartbattery device having an A/D converter with a single positive powersupply that is capable of bipolar operation for converting both positiveand negative analog signals representing battery charge and dischargecurrents, respectively.

Another object of the instant invention is to provide a smart batterydevice as above wherein the analog and digital components of the ASICcomprise CMOS semiconductor technology designed for improved accuracy,and high A/D converter resolution with minimal power consumption.

Still another object of the present invention is to provide a smartbattery device having a microprocessor such that, when nominallydischarged, will place itself in a sleep mode with virtually no powerconsumption.

Yet a further object of the present invention is to provide a smartbattery device that includes a microprocessor with RAM memory, andcomprises means for retaining RAM memory contents when the device is ina sleep mode.

Yet still a further object of the invention is to provide a smartbattery device that comprises short circuit protection means forpreserving RAM memory contents when battery is temporarily shortcircuited.

Another object of the instant invention is to provide a smart batterydevice that includes a ROM memory that is manufactured by a process thatfacilitates the programming of ROM in an upper or respectively laterproduced layers.

Yet furthermore, an object of the instant invention is to provide asmart battery device that includes a ROM memory device whereby theprogramming of the ROM is effected in a metal mask.

Furthermore, an object of the instant invention is to provide a smartbattery device having incorporated therein an error treatment algorithm,for taking into account measurement errors, interpolation from look-uptables, etc., wherein the errors are considered to be a function oftime. It is contemplated that if a total error is larger than apredetermined value, certain operating modes are disabled, and, inparticular, variables are substituted by default values to result in asmaller error. In case of displayed information, such as LED batterypack display, the error can be additionally taken into account, fore.g., a quantity of: capacity--total error in capacity, may bedisplayed. If an error that is too big is produced, the end criterionfor determining end of charge condition may be changed, for e.g.,using--a change in battery voltage instead of the error influencedcriterion.

These and other objects of the present invention are attained with asmart battery device which provides electrical power and which reportspredefined battery parameters to an external device having a powermanagement system, wherein the battery includes:

(a) at least one rechargeable cell connected to a pair of terminals toprovide electrical power to an external device during a discharge modeand to receive electrical power during a charge mode, as provided ordetermined by said remote device,

(b) a data bus for reporting predefined battery identification andcharge parameters to the external device,

(c) an analog means for generating analog signals representative ofbattery voltage and current at said terminals, and an analog signalrepresentative of battery temperature at said cell,

(d) a hybrid integrated circuit (IC) having a microprocessor forreceiving the analog signals and converting them to digital signalsrepresentative of battery voltage, current and temperature, andcalculating actual charge parameters over time from said digitalsignals, said calculations including one calculation according to thefollowing algorithm:

    CAP.sub.rem =CAP.sub.FC -ΣI.sub.d Δt.sub.d -ΣI.sub.s Δt.sub.s +Σε.sub.c I.sub.c Δt.sub.c

wherein ε_(c) is a function of battery current and temperature; andI_(s) is a function of battery temperature and CAP_(FC),

(e) a data memory defined within said hybrid IC for storing saidpredefined battery identification and actual charge parameters, evenwhen nominally fully discharged, said charge parameters including atleast full charge capacity and remaining capacity,

(f) a bus controller defined within said hybrid IC for sending batterymessages to said remote device over said data bus, said messagesincluding said predefined battery identification and said actual chargeparameters.

Superimposed on this equation is reset logic, to be explained below,that self corrects the value of CAP_(FC) with a capacity calculation ateach end of full charge (EOC) and each end of full discharge.

Further benefits and advantages of the invention will become apparentfrom a consideration of the following detailed description given withreference to the accompanying drawings, which specify and illustratepreferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic block diagram of a smart battery deviceconnected to a host computer and battery charging device.

FIG. 2(a) is a simplified block diagram of the smart battery device andconnector, including a pinout diagram of an Application SpecificIntegrated Circuit (hybrid IC) used in the present invention.

FIG. 2(b) illustrates a simplified block diagram of the hybrid IC 32that includes the microcontroller of the smart battery device of theinstant invention.

FIG. 3 is a general flow diagram illustrating the primary functionalfeatures of an algorithm and method for controlling the smart batterydevice of the instant invention.

FIG. 4 illustrates a general schematic diagram of the A/D converter 60.

FIG. 5(a) illustrates a schematic sketch of dc voltage shifting circuitarrangement.

FIG. 5(b) illustrates a second embodiment of the dc voltage shiftingcircuit arrangement.

FIG. 6 is a schematic sketch of the circuit arrangement in the A/Dconverter 60.

FIG. 7 is a phase diagram in the operation of the A/D converter pursuantto FIG. 6.

FIG. 8(a) illustrates the timing of the operating cycles under normaland sample mode operating conditions.

FIG. 8(b) illustrates the approximate time durations for the variousmeasurements per operating cycle.

FIG. 9(a) illustrates a schematic sketch of a sample transitionarrangement for the ROM included in the smart battery device; and

FIG. 9(b) is a schematic sketch of the transistor arrangement of an ROMprogrammed pursuant to the prior art.

FIG. 10 is a detailed schematic of the power-on reset 85 and RAMde-latching circuit 85'.

FIG. 11 illustrates a detailed schematic diagram of the comparatorwake-up circuit 80.

FIG. 12 is a flow diagram illustrating the IUT (current, voltage, andtemperature) calculation program 200.

FIGS. 13(a) and 13(b) are flow diagrams illustrating the sequentialprocesses 151 programmed in the microprocessor for calculating thecurrent capacity and the amount of battery self discharge for the smartbattery of the instant invention.

FIG. 13(c) illustrates the integration program 400 for calculating theamount of battery charge or discharge flowing into or out of itsterminals.

FIGS. 14(a) through 14(c) are flow diagrams illustrating the sequentialprocesses 500 programmed in the microprocessor for determining batteryend conditions when the battery charging is in a capacity increasingstate.

FIG. 14(d) illustrates a flow diagram of the learn number of cellsprogram 700.

FIGS. 15(a) and 15(b) are logic flow diagrams illustrating thesequential processes 600 programmed in the microprocessor fordetermining battery end conditions when the battery is in a capacitydecreasing state.

FIG. 16 illustrates a logic flow diagram of the handle request routinethat is invoked when there is communication between the smart batteryand the host computer or battery charger.

FIG. 17 illustrates a detailed logic flow diagram of the write blockroutine for writing data to the smart battery.

FIG. 18 illustrates a detailed logic flow diagram of the read blockroutine for reading data from the smart battery.

FIGS. 19 illustrates a flow diagram describing the logic steps invokedby the smart battery system when broadcasting an alarm condition to anexternal device.

FIG. 20 illustrates a logic flow diagram describing the steps invoked bythe smart battery system when broadcasting a charge condition to abattery charger.

FIG. 21 illustrates a logic flow diagram describing the steps invoked bythe smart battery system when broadcasting a message.

FIG. 22(a) is a three-dimensional graphic representation of look uptables that depict predicted residual capacity values as a function ofdischarging current and temperature.

FIG. 22(b) is a three-dimensional graphic representation of look uptables that depict the amount of self-discharge current (vertical axis)as a function of relative battery state of charge and temperature.

FIG. 22(c) is a three-dimensional graphic representation of chargeefficiency look-up tables showing charge efficiency factors as afunction of relative state of charge, charging current, and temperature.

FIG. 23 illustrates two voltage versus time graphs, a and b, comparingcalculated battery capacity characteristics at various dischargingcurrent rates for a six (6) cell battery pack.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The smart battery device of the present invention is intended for usewith an intelligent host device such as a portable computer, portablevideo camera or cellular telephone having a system management bus and asmart charger, or an intelligent host device having a system powermanager that can receive and send data over a system management bus.

A representative example of such a system is illustrated in FIG. 1,wherein the smart battery 10 is connected to a power plane 12 to supplyand receive electrical energy over the power plane, and a systemmanagement bus 14, which is a bi-directional modified I2C data bus(communication interface) that communicates with a host device 16 whichmay be a portable computer.

The host device 16 may be powered by the smart battery 10, or by thesystem power supply 18 and a conventional AC source 20. A system powersupply or power management system also communicates with a smart charger22 which may be used to determine the rate and duration of charge sentto the smart battery by the power supply. Smart charger 22 alsocommunicates with the system management bus 14, and may receive atemperature signal representative of battery cell temperature on aseparate line 24. A detailed functional description of the systemmanagement bus 14 (bi-directional modified I2C data bus) can be found inthe Intel\Duracell System Management Bus Specification, Rev 0.95, (April1994).

The power management system 18 may supply or draw power to/from thesmart battery 10 over power plane 12, depending upon the state of chargein smart battery 10, and depending upon the presence or absence of powerat AC source 20.

The smart charger 22 may periodically poll the smart battery 10 forcharge characteristics, and adjust output to match a smart batterycharge request. Optionally, and if selected by the user of the hostdevice, the smart charger 22 can override the smart battery's chargerate request and charge the smart battery at a higher or quick chargerate. The user of the host device does not necessarily need to overridethe smart battery's request. As will be explained in greater detailbelow, the smart battery may periodically broadcast the desired chargingcurrent, or the smart charger 22 polls the smart battery for a chargingcurrent. The host or the charger need not comply with the smartbattery's request and can provide a greater or lesser amount of powerthan requested.

The host device 16 may communicate with the smart battery over thesystem management bus 14 and request information from the battery foruse in the system power management scheme, thereby providing the user ofthe host device with information about the battery's present state andcapabilities. The host device 16 will also receive notice of criticalevents, including alarm conditions, remaining capacity below a user setthreshold value, a remaining run time below a user set threshold value,or an end of discharge signal. The alarm conditions include but are notlimited to overcharging, overtemperature, a remaining charge capacitybelow a predetermined or user set capacity, or a run time below apredetermined or user set run time remaining.

As will be hereinafter explained in greater detail, the smart batterycan report out an instantaneous current value being drawn from thebattery, current values averaged over predetermined time intervals,present temperature and present voltage.

The smart battery may also report out a number of battery statusindicators, indicating whether or not the battery is charging ordischarging, that charging is complete, or that the battery is fullydischarged.

In addition, the smart battery can provide calculated values includingrun time remaining at a present current usage, a run time remaining atan average current use, a run time remaining at optimal current use, anda predicted run time remaining at a host device selected current level(discharge rate).

The smart battery device 10 is also provided with a read-only memory(ROM) that is manufactured to contain a set of predefined batteryidentification parameters which may include manufacturer data, cellchemistry, design capacity, design voltage, and a unique deviceidentification number. The predefined battery identification parametersare available, for either the host device or the smart charger, toassist them in the selection of optimal usage and charge parameters forthe smart battery.

The smart battery is also capable of recommending a desired chargecurrent, reporting a time remaining to full charge, a battery capacityavailable at full charge, and the number of times the battery has beencharged or discharged.

The smart battery of the present invention utilizes a hybrid integratedchip (IC) containing an embedded microprocessor and a novel analog todigital converter which receives analog signals from the battery andconverts them to digital signals representative of battery voltage,current and temperature. The smart battery microprocessor thencalculates actual charge parameters over time from these digital signalsaccording to a predetermined algorithm in which CAP_(rem) is theremaining capacity of the battery which is continuously assigned a newvalue to reflect adjustments for effective charge, discharge, and selfdischarge.

The charge delivered to the battery is measured, and adjusted by anefficiency factor which is a function of current, temperature, andrelative state of charge. It should be mentioned that the remainingcapacity, CAP_(rem), and the relative state of charge, SOC, representthe same thing (remaining battery capacity) and differ in that relativestate of charge is indicated as a percentage of the last full chargecapacity. The charge efficiency is a value determined as a function ofthe above variables and may be derived from a look up table, hereinafterdescribed with respect to FIG. 22(c), or calculated from a formula whichprovides a stepwise approximation of charge efficiency behavior,depending upon current, temperature and state of charge. It isunderstood that the charge efficiency factor can be obtained from aresponse equation or interpolation between several different valuesstored in memory.

Likewise, the remaining battery capacity CAP_(rem) is decremented by themeasured discharge rate over time. A predictive model of residualcapacities determines expected CAP_(rem) for a present current andtemperature. This predictive model may also estimate when the batteryvoltage will drop to a predetermined cut-off voltage for the presentrate of discharge. This residual capacity model may be calculated from aformula or obtained from a look up table, which includes values ofresidual capacities as a function of discharge current and temperature.

Finally, CAP_(rem) is also adjusted by subtracting self discharge. Selfdischarge is calculated as a function of temperature and state ofcharge, and is always subtracted from CAP_(rem), regardless of whetherthe battery is discharging or being charged. Self discharge may bederived from a look up table of empirical models of identical cellchemistry that predict self discharge as a function of temperature andstate of charge, or may be calculated by the microprocessor.

As will be hereinafter explained in greater detail, CAP_(FC) is alearned value which is self correcting because of reset logicincorporated in the capacity algorithm. The capacity algorithm takesactions on four types of end of charge (EOC) signals, including anegative voltage slope at a full charge voltage, a temperature rise thatexceeds a predetermined rate, or a calculated state of charge that isequivalent to a value of 100% to 150% of the previous CAP_(FC) value, ifan optimal charging current has been used, or a high temperature limitvalue. When one of the first three of the above four types of conditionsis encountered, the reset logic resets CAP_(rem) to the previousCAP_(FC) value, sets a fully charged status flag, and, signals the hostdevice and charger to terminate charge. If the high temperature limit isreached, only a signal to terminate charge is invoked.

The charge algorithm terminates its integration of the present dischargestate when it reacts to an end of discharge (EOD) signal between 0.9volts/cell and 1.1 volts/cell and preferably 1.02 volts per cell. Atthat point the algorithm resets CAP_(rem) to a new learned value ofresidual capacity, as determined from the integration of the dischargecurrent, as a function of discharge current and temperature.

As will be hereinafter explained in greater detail, the reset logic willreset CAP_(FC) as a function of which EOD signal was acted on. Thus anew CAP_(FC) value for the smart battery's actual capacity is learnedafter each full discharge cycle, as a function of the last fullyintegrated battery discharge cycle. The smart battery 10 of the presentinvention is thus able to self correct CAP_(FC) within one full cycle toreadjust its capacity at each EOC and EOD, and effectively relearn fullbattery capacity within a single cycle, even if all prior batteryhistory has been extinguished by virtue of a catastrophic memoryfailure. The smart battery of the present invention is therefore able toaccurately predict actual capacity, and typically is able to correctlypredict the remaining run time to empty within a few minutes for a 2400maH battery.

Smart battery 10 of the present invention is more fully illustrated inFIG. 2(a) which is a simplified block diagram of the smart battery, anadvanced design multi-pin connector, and a battery module 28 whichincludes a pinout diagram of the hybrid ASIC 32 used in the presentinvention. As illustrated in FIG. 2(a), the smart battery device 10includes a plurality of rechargeable cells generally indicated at 26which may be Nickel Metal Hydride (NiMH) or Nickel Cadmium (NiCad)cells.

For the purposes of an illustrative but not limiting example, in thefollowing specification, 6 NiMH cells having a nominal 2400 maHcapacity, will be assumed. Such an arrangement of cells is particularlyappropriate for powering a portable computer.

A suitable advanced design multi-pin battery connector 30 is used toconnect the smart battery to a host device 16 or power supply 18, aspreviously described with respect to FIG. 1. The multi-pin connector 30includes a positive power supply terminal 31 which is connected to thepositive terminal of the first cell, and a negative power supplyterminal 33 which is connected to the negative terminal of the lastcell. A plurality of rechargeable cells may be connected in seriestherebetween as illustrated in FIG. 2(a).

The smart battery module 28 includes a hybrid IC 32 containing amicroprocessor 50 (FIG. 2(b)) and a plurality of sensor means forgenerating analog signals representative of battery voltage, current andtemperature. The module also includes a series of four (4) LEDS 34driven by an LED drive circuit 53 and a switch 35 which may be manuallyactuated by an end user to determine the state of charge in the batteryeven when the battery module has been removed from the host device 16.The LEDS 34 may be used to represent a relative state of charge (SOC) ina logic scheme as follows: if the state of charge is greater than 75%(or less than 100%) then all 4 LEDS are illuminated; if the SOC is from50% to 75%, then 3 LEDS are illuminated; if SOC is from 25% to 50%, then2 LEDS are illuminated; if SOC is from 10% to 25%, then 1 LED isilluminated, and if SOC is less than 10%, a single LED is flashing. Asmentioned above, relative SOC is remaining capacity relative to lastfull capacity.

As shown in FIGS. 2(a) and 2(b), the hybrid ASIC 32 also includes anexternal crystal 36 operating at a fixed frequency which is used as atime base for integration of battery current over time, and to ensurestable start up after a prolonged standby period when power is reappliedto the smart battery 10. The smart battery of the present inventionutilizes two separate oscillators, a low power RC oscillator 48 formedwithin the hybrid IC 32 and used as an operating clock for the hybrid ICand the A/D converter 60 therein, and the external crystal 36. As willbe hereinafter described in greater detail, the external crystal 36 isused to restart the measurement period after each predetermined intervalto provide for accurate measurements and integration of batteryconditions, regardless of battery temperature, which can adverselyaffect the accuracy of the internal oscillator. The frequency value ofexternal crystal 36 may range from 10 kHz to 66 kHz, preferably at 32kHz and the frequency value of oscillator 48 may range from 450 kHz to460 kHz.

The hybrid IC 32 includes a MIKRON GmbH low cost, high performance, CMOS8 bit microcontroller (μP) 50 with an advanced RISC architecture. Areduced set of 32 instructions that are all single cycle instructions(except for program branches which are two cycles), and a Harvardarchitecture scheme achieves a high level of performance with minimalpower drain. The microprocessor operates at a clock input anywhere fromDC to 10 MHz with 12 bit wide instructions and 8 bit wide data path. Afree programmable Counter/Timer circuitry is provided as well as a freeprogrammable Watchdogtimer. Additionally, the microprocessor isaddressable in direct, indirect, and relative addressing modes. Themicroprocessor 50 is commercially available from Mikron Gmbh, located atBreslauer Strasse 1-3, D-85386, Eching, Germany, and is available in theU.S.A. through MICROCHIP Technology, Inc., Chandler, U.S.A.

The hybrid IC 32 also includes a plurality of analog circuits which areused, in combination with external analog sensors, to generate digitalsignals representative of battery voltage, current and temperature aswill be hereinafter explained.

For example, as shown in FIG. 2(a) battery voltage is obtained from avoltage divider circuit which includes resistors R1 and R2 which areinternally switched by a NMOS transistor within the hybrid IC 32 toprovide voltage measurement during a small portion of each measurementinterval, thereby minimizing current drain on the battery cells 26.

The measurement of battery temperature is accomplished with anNTC-thermistor, illustrated as R_(NTC1) in FIG. 2(a), which variesresistance as its temperature varies. A resistor R3 is connected inseries to form a voltage divider circuit between V_(ASS), (negativeanalog power supply voltage) V_(TEMP),(the temperature voltage input)and V_(REFT), which is a reference voltage applied to thethermistor/resistor string by the hybrid ASIC 32 at pin V_(REFT). Thetemperature voltage input is measured at V_(TEMP) according to thefollowing formula: ##EQU1## wherein the NTC1 value may be 10 kohms at25° C. and varies with temperature. If desired, a look-up table with aplurality of temperature values and a plurality of V_(TEMP) values maybe defined to calculate the battery temperature, and between thesevalues, the temperature is linearly interpolated by the microprocessorwithin IC 32.

The measurement of battery current is measured through a shunt resistor,illustrated in FIG. 2(a) as R_(shunt), that is connected in series withthe battery cells and negative terminal 33 of cell pack 26. The shuntresistor is of small value, but may range anywhere from 1 mohm to 200mohms depending on the number of cells and expected usage of thebattery. The voltage drop across the shunt is sensed between V_(SHUNT+),the shunt resistor positive input pin of ASIC 32, and V_(ASS), thenegative analog power supply voltage.

As shown in FIG. 2(b), whenever the analog signals representing batteryvoltage, current, and temperature are obtained, they are input into anASIC multiplexor or switching network 55 which enables only one analogsignal at a time to be input to the A/D converter 60 for digitalconversion. The switching network acts in conjunction with digital logiccircuitry for informing the A/D converter, via line 55', shown in FIG.2(b), of the amount of integration cycles to perform depending upon thetype of measurement to be converted. For instance, more integrationcycles are needed when making a current measurement conversion to ensurea higher bit resolution as compared to when a voltage or temperaturemeasurement is being converted, as will be explained in further detailbelow with respect to FIG. 8(a).

A general schematic diagram of the A/D converter 60 is shown in FIG. 4.In the preferred embodiment, the A/D converter 60 is a bipolar, highresolution, incremental sigma-delta converter and consists of threeparts: a bandgap reference circuit 62 which provides a preset analogvoltage which is used as an analog ground for the A/D; a voltage dividernetwork 64 which divides the present voltage to the analog voltageswhich are used as the full-scale voltage for the A/D; and a sigma deltacircuit 66 for converting the analog signal to a digital word output atline 69. A/D control circuit 68 having a clock input from the ICoscillator, provides the control for the sigma delta converter which hasa different degree of resolution depending on the type of measurement.For instance, in one embodiment of the invention, the A/D converter wasconfigured as having a resolution of 13 bits and a conversion timeranging from 300 to 400 msec for current measurements, and wasconfigured as having a resolution of 10 bits and a conversion timeranging from 30 to 60 msec for voltage and temperature measurements. Thetiming diagram for the voltage, current, and temperature measurements ineach operating cycle is illustrated as 58a in the timing of operatingcycles diagram of FIG. 8(a), as explained below.

In one embodiment of the invention, the voltage divider circuit 64 ofthe A/D converter divides the preset bandgap reference voltage into thefollowing full scale voltages: a 150 mV signal used as the full scalevoltage for the battery current measurement; 150 mV, 250 mV, or 350 mVsignals used as the full-scale voltage for the battery pack voltagemeasurement and dependent upon the number of battery cells; and 150 mVused as the full-scale voltage for the battery temperature measurement.These values are illustrative and may vary as battery design varies.

The A/D converter of the smart battery device utilizes a sigma-deltaconverter circuit 66 as explained above in view of FIGS. 4 and 6.Details of the sigma-delta converter circuit 66 capable of bipolarconversion are explained hereinbelow in view of FIGS. 5(a),5(b) andFIGS. 6 and 7. FIG. 6 particularly illustrates a switching capacitornetwork for receiving positive and negative voltage values, indicated asV_(IN) in FIG. 6 for input into an integrator circuit 88 and comparatorcircuit 89 for output into control and logic circuit 68. In thereference, Jacques Robert et al., (1987) "A 16-bit Low-Voltage CMOS A/DConverter", IEEE Journal of Solid-State Circuits, Vol. sc-22, No. 2,157-159, an incremental (integrating) sigma-delta converter implementing4-μm CMOS, switched capacitor technology similar to that implemented inthe A/D converter of the smart battery device is disclosed. What isdescribed in the reference is a simplified, unipolar A/D converter thatis largely insensitive to variations in clock frequency and clockwaveforms due to the fact that all signals are represented by charges,rather than currents, as in the switched capacitor integrator that formsthe core of the converter.

In the prior art, to measure positive and negative input voltages, anegative power supply is necessary in addition to the positive voltagesupply. Thus, where it is desired to measure negative voltages (orcurrents) such as smart battery discharging current, external components(such as inverters) and circuitry that consume extra power are required,and the prospect of utilizing such circuitry for the low powerapplication such as needed in the smart battery device of the instantinvention, is diminished. Instead, to overcome this drawback, the A/Dconverter 60 of the instant invention does not utilize a negativevoltage power supply, but makes use of an available on-chip A/D bandgapreference voltage "AGND" to be used as a virtual ground. The concept ofutilizing a "virtual ground" is based on the fact that a voltage storedon a capacitor can be transferred to another d.c. voltage referencepoint using analog switches with virtually no loss of charge.

In FIG. 5(a) there is represented a first embodiment of the dc voltageshifting circuit arrangement, consisting of three switches S1 throughS3, and four connectors A1 through A4 and a capacitor C1 (with thecapacitance C1). The connectors A1 through respectively A4 are at thepotentials φ₁ through respectively φ₄. As shown in FIG. 5(a), the switchS1, and the combination of parallel-connected switches S2 and S3 areconnected to opposite terminals of the capacitor C1.

In the following there is described the operation of the inventivecircuit arrangement. At the beginning, the switches S1 and S2 are closedand the switch S3 is open. The capacitor charges itself up due to thevoltage differential φ₁ -φ₂ and stores a charge C1×(φ₁ -φ₂).

In the next step of the inventive process, the switches S1 and S2 areopened and one pole of the capacitor is connected through switch S3 witha potential φ₃. Present at the capacitor C1 is now a voltage φ₃ +(φ₁-φ₂) which can be tapped off through connection with the connectors A3and A4 which lie on the potentials φ₃ and φ₄.

In FIG. 5(b) there is now represented a further embodiment of the dcvoltage shifting circuit whereby an additional switch S4 is providedwhich, when open, prevents the presence of a potential φ₁ at the tappingoff of the voltage φ₃ +(φ₁ -φ₂) present at the connectors A3 and A4,when switch S1 is closed.

In FIG. 6 there is illustrated the schematic circuit diagram of theinventive circuit arrangement in a switched capacitor A/D converter. TheA/D converter 66 possesses an operational amplifier 88 which is utilizedas an integrator, and an operational amplifier 89 which is utilized as acomparator. The non-inverted input of the comparator 89 by means of theline 91 stands in connection with the output of the integrator 88. Theinverted input of the comparator 89 and the non-inverted input of theintegrator 88, are connected with a reference potential AGND, (analogground=1.25 volt). The output of the comparator 89 is "high", in theevent that the output voltage of the integrator 88 is higher than thereference voltage AGND and "low" in the event that the output voltage ofthe integrator 88 is lower than the reference voltage AGND. By means ofthe lines L1, L2, L3 and L4, the integrator 88 or, in essence, theinverted input and the output of integrator 88 have connected inparallel therewith a capacitor C2 with a capacitance C2. The capacitorC2 has a switch SR connected in parallel therewith through lines L1 andL5, which can effectuate a discharge of the capacitor C2. Through a lineL6, the inverted input of the integrator 88 stands in connection, bymeans of a switch S5 and a line L7, with a capacitor C1 having thecapacitance C1. A line L8 connects the line L7 through a switch SI andthe line L4 with the output of the integrator 88. The line L9 connectsthe pole of the capacitor C1 facing towards the integrator 88 in FIG. 6with a line L10, which stands in connection through the lines L11, L12and respectively L13, with the switches S4, S7 and, respectively S6.Connected to the other pole of the capacitor C1 is a line L14, which isconnected through the switch S3 with the reference voltage AGND=1.25volt. A line L15 stands in connection with line L14 and connects throughthe lines L16, L17, and respectively L18, the pole of the capacitor C1,which faces away from the integrator 88 in FIG. 6, with the switches S2,S1, and respectively, S8. The internal mass of the chips V_(SS) =0 voltstands through the lines L19 and, respectively, L20, in connection withthe switches S8, respectively, S6. In this manner, through suitableopening and closing of the switches S8 and S6, the voltage V_(SS) can beapplied to both poles of the capacitor C1. The input voltage V_(IN)which is to be digitized stands in connection with the switches S1 and,respectively, S7, through lines L21 and, respectively, L22. In thismanner, through suitable opening and closing of the switches S1 and S7,the input voltage V_(IN) can be applied to either of the two poles ofthe capacitor C1. The reference voltage V_(REF) which determines theresolution of the A/D converter is connected through lines L23 and,respectively, L24 with the switch S2 and, respectively, S4. In thismanner, the reference voltage V_(REF), which, for example, consists of150 milli- volt, can be applied to one of the two poles of the capacitorC1. The switches S1, . . . ,S8, SR and SI are preferably CMOS switches,especially CMOS transmission gates. The connection of the input voltageV_(IN), the reference voltage V_(REF) and the mass V_(SS) with the inputcapacitor C1 of the A/D converter is known in the technology.Inventively there is connected through the switch S3 a reference voltageAGND=1.25 volt (≠V_(ss) =0 volt) to the input capacitor C1. Similarly,through the inventive circuit, V_(IN), V_(REF) and AGND can be appliedto both sides of the input capacitor C1, which presently causes acharging up at different polarity of the capacitor C1.

In FIG. 7, there is illustrated the operation of the A/D converter in aphase diagram. Thereby, S1 through S8, SR and SI designate the switchesof the A/D converter 66 pursuant to FIG. 6, and CK is the pulse signalof the comparator 89 in FIG. 7. CK' represents a further tapped-offpulse signal.

In the diagram, the switch conditions fluctuate between 0 and 1, whereby1 signifies that the switch is closed, whereas 0 stands for the openedswitch. The operation of the A/D converter can be divided into fourphases which are designated with I, II, III and IV whereby I designatesa RESET or resetting phase; II an integration phase, III and invertingphase and IV an integration phase of the input voltage of reversepolarity or sign. The cycle is more finely subdivided into stepsi, - - - xiv. As shown as step i in FIG. 7, during the reset phase I,only the switch SR is closed, whereas all other switches are opened.This causes a discharge of the capacitor C2. At the beginning of phaseII, as indicated as step ii, in FIG. 7 the switches S1 and S6 areclosed, whereas all remaining switches remain further open. This causesa charging up of the capacitor to a charge ΔQ=C1×(V_(IN)-V_(SS))=C1×V_(IN). In step iii, the switches S3 and S5 are closed,whereas all other switches remain open. One pole of the capacitor is nowset to the potential AGND, whereas the other pole of the capacitor C1,through closing of the switch S5, stands in connection with thecapacitor C2. There now takes place a charge transfer from the capacitorC1 to the capacitor C2. Inasmuch as the integrator of 88 resultinglycauses the two input potentials to be equalized, there is present at theoutput 91 of the integrator 88 the output voltage V_(OUT)equal-(C1/C2)×V_(IN) +AGND. In step iv all switches are opened and thecomparator pulse CK is 1, meaning, the comparator 89 carries out acomparison between V_(OUT) and AGND. Upon the result of this comparisonthere now depends the further cycle. The representation of the switchconditions in step v must be understood in the following manner: In stepv the switches S2 through S8 are not closed, but the switches S2 and S6are closed, and S1, S3, S4, S5, S7, SR and SI are open, in the eventthat the output of the comparator is 0, in effect "low", while theswitches S4 and S8 are closed and S1, S2, S3, S5, S6, S7, SR and SI areopen when the output of the comparator is 1, meaning, "high", and inother instances remain open. When the output of the comparator is 0,meaning the output voltage V_(OUT) is lower than AGND, then the switchesS2 and S6 are closed. At the capacitor C1 there are now present V_(REF)and V_(SS). In the instance in which the output of the comparator is 1,meaning, V_(OUT) is higher than AGND, then the switches S4 and S8 areclosed, whereby similarly V_(SS) and V_(REF) are present at the twopoles of the capacitor C1, but with the reverse sign or polarity than inthe instance in which the output of the comparator is 0. In step v, theswitches S1, SR and SI are opened, and in step vi, the switches S3 andS5 are closed (compare step iii) which causes the capacitors C1 and C2to be interconnected. As in step iii, voltage AGND is applied to onepole of the capacitor C1. There again, in turn takes place a chargetransfer between the capacitors C1 and C2, as result of which avoltage-(C1/C2)×V_(REF) +AGND is added to or, respectively, subtractedfrom that of the output voltage of the integrator 88, in accordance withthe result of the comparison by the comparator in step iv. During thesteps i through vi of phase II there is processed an input voltage whichis phase shifted with respect to AGND, with a reference voltage which isshifted relative to AGND. Similarly, at the non-inverted input of theintegrator 88 and the inverted input of the comparator 89 there liesAGND, which causes that the output voltage is referenced to AGND andcauses a comparison by the comparator 89 not with V_(SS) =0 voltage, butwith AGND=1.25 volt.

In the following there is now discussed phase III consisting of stepsvii to ix. In this phase, a sign or polarity reversal is implemented forthe output voltage V_(OUT) of the integrator 88 with reference to AGND.During the entire phase III the switch S3 is closed. The closure of theswitch S3 during the phase III causes the voltage AGND to be applied toone pole of the capacitor C1, as a result of which the voltage V_(OUT)is also inverted with regard to AGND and not with regard to V_(SS) =0,as in the known A/D converters. In step vii there is now closed theswitch SI, whereas all remaining switches are open, except switch S3.This causes that the voltage V_(OUT) is temporarily in the capacitor C1,such that in step viii all switches are opened except switch SR. Theswitch SR is in effect closed, which causes a discharge of the capacitorC2. In the step ix the switch S5 is closed additionally to switch S3,while all remaining switches are opened. This causes that the negativevoltage which is phase shifted at AGND is present at the output of theintegrator 88. The negative sign is obtained, as previously through thecharge transfer from the capacitor C1 to the capacitor C2. In step x ofPhase IV, the switches S7 and S8 are closed, whereas all remainingswitches are opened. Compared with the step ii the input voltage V_(IN)is present with a reverse polarity at the capacitor C1. This causes achange in the sign of the integration of the input voltage, which isalso well recognizable in FIG. 6 of the above mentioned publication ofJacques Robert et al. The steps xi through xiv correspond with the stepsiii through vi, meaning, there is implemented an integration of theinput voltage (only due to step x with a reverse sign of V_(IN)), and inaccordance with the result from the comparator 89 in step xii V_(REF) isadded or, respectively, subtracted after the integration (in caseC1=C2). For a 14-bit A/D-converter, after implementing step i there iscarried out phase II ( 2¹⁴ -2 (for the phases I, and III)!:2=8191times), as well as phase IV. The output of the comparator is connectedto a up/down counter, which each time, in accordance as to whetherV_(REF) is added or subtracted, increases or lowers its count conditionby 1. The result of the counter is then a 14-bit representation of theratio of V_(IN) to V_(REF). The phases III and IV are necessary sincethrough the integration with reverse signs of V_(IN) offset errorsencountered in, for example the operational amplifiers, are reported or,respectively eliminated.

The multi-pin connector 30 includes two pins for the system managementbus interface 75, which include a serial clock I/O line 38 and abidirectional serial data I/O line 40. These lines are connected to theSMBCLK and SMBD data pins, respectively, of the hybrid IC 32. Asexplained generally above, and, in greater detail below, the smartbattery module 28 communicates with the host device 16 and the smartcharger 22 over the system management bus and data line 40 tocommunicate both stored battery parameters and calculated batteryparameters.

The smart battery 10 also includes a separate thermistor R_(NTC2) whichis connected across the negative terminal of multi-pin connector 30 anda temperature or thermistor line 42. Thermistor R_(NTC2) may be usedindependently by the smart charger 22 to determine battery temperature,in a manner similar to that previously described with respect toR_(NTC1).

A positive digital power supply voltage is obtained from the pluralityof rechargeable battery cells 44, and supplied to the hybrid IC throughpin V_(DD) as the positive power supply voltage for the chip. It shouldbe understood that the supply voltage for the hybrid IC does notnecessarily have to be obtained at the battery midpoint 46, but shouldbe obtained at a point from the battery cells in order to receive avoltage of approximately 3 to 4.8 volts, i.e., the equivalent voltage ofthree (3) cells. As will be hereinafter explained in greater detail, theuse of a battery midpoint for the positive voltage supply enables thehybrid IC to remain powered even when the battery is accidently shortedand removed from terminals 31-33, and enables the A/D converter 60 todetermine whether the battery is discharging or being charged as willhereinafter be explained in greater detail. Suitable fuse elements (oneof which is shown in FIG. 2(a)), and a positive temperature coefficient(PTC) elements (one of which is shown in FIG. 2(a),, are provided inseries with the battery pack cells to protect the battery from very highcurrent and excessive temperatures caused by a temporary short circuitacross the battery terminals or other thermal event.

As shown in FIG. 2(b), the hybrid IC 32 further includes RAM memory 65which can store up to 128 8-bit registers for communication ofcalculated battery parameters, and a ROM memory 67 for storing look-uptable values utilized in the battery capacity calculation algorithm(explained in detail below). The exact amount of RAM, ROM, and programROM memory is a design choice, and these values change as the ratiobetween calculated and preset parameters vary.

As shown in FIG. 2(a), the addition of capacitor C4 acts as a buffer tomaintain the integrity of the RAM memory contents in the case of abattery short-circuit or temporary power loss. Preferably, the capacitorC4 is connected to the negative analog voltage supply terminal, and itsvalue is chosen to ensure that a source of supply voltage is supplied tothe embedded memory (RAM) for a time dependent upon the RAM leakagecurrent. In the preferred embodiment, the power to RAM memory isunlatched if a temporary short circuit condition exists, However,capacitor C4 preferably of capacitance 330 nF, provides a source voltageto the RAM for a period of time necessary for the PTC element to ramp toa high resistance value. The PTC element will create a high impedancebetween battery terminals when a short circuit across the battery packterminals creates a high circuit drain.

The hybrid IC 32 further includes up to 4 kbytes of additional ROMmemory 70 for addressing and storing the various algorithms,subroutines, manufacturer data, and data constants utilized by the smartbattery module for calculating the battery capacity, sending messagessuch as alarms and battery charger control commands etc., and handlingmessage requests from external devices.

The programmable ROM generator is implemented by means of a metal mask(not shown) as opposed to conventional ROM generation by means ofdiffusion masking. In accordance with the information which was to bepermanently stored, transistors were generated in a matrix arrangementthrough diffusion, whereby the information was coded in the planethrough the distribution of the transistors in the diffusion step. Thus,the ROM generator generates in effect, a ROM matrix, whereby thepresence or respective absence of an MOS transistor stands for a logic"O" respectively "1." A disadvantage of a ROM matrix with theprogrammable level of diffusion is that the diffusion process, which isincorporated as one of the first steps of a CMOS process, can not bechanged when there is a change in ROM contents, thus, renderingimpossible the production of wafer stock for a particular type of ROM.

By contrast, the advantage of a ROM matrix programmable in a metal layeris that wafer stock with the same basic layers up to the metal may befabricated. Thus, a microprocessor family with different ROM contentscan be realized with low cost and fast turn around time. Additionally,the pre-manufacture of a portion of the ROM with the flexibility ofprogramming in application specific information in the upper orrespectively later produced layers, is possible.

The hybrid IC chip itself may comprise thirteen or fourteen layers, withthe 9^(th) or 10^(th) layer (i.e. one of the upper layers) being a layerof metal, wherein the distribution of the metal is characteristic forthe storing contents of the ROM. Thus, in the hybrid IC ROMmanufacturing process, nine (9) layers are grown and the next four ROMprogramming layers are grown dependent upon the customer's particularneeds (i.e., special properties of the battery pack).

FIG. 9(a) shows a ROM matrix with the metal layer as a programmablelayer. A MOS transistor, e.g. 71(a) for the matrix is always present onthe matrix and will either serve as a logical "0" or "1" . Specifically,FIG. 9(a) schematically illustrates the ROM 67 of the smart batterydevice that is programmed according to the unique process as follows:The represented ROM matrix consists of eight word lines 67a andindicated as WZ0, . . . , WZ7 and 8 spaces 67b and indicated as SP0, . .. , SP8, whereby the spaces SP1,SP3,SP5,SP7 connect with a virtualground line 73. At each location of the matrix, there is produced atransistor in the diffusion step, three transistors 71a, 71b, and 87 ofthe matrix are shown in FIG. 9(a). For the programming of a logic "0,"in a respective word line, the drain or respective source electrodes ofa transistor are connected to a metal mask with the corresponding sourceor respectively drain electrodes of the joining transistors or thejoining transistor. The drain or respective source electrodes of such atransistor are connected with the gap lines or, respectively, thevirtual ground lines 73. Transistor 71a in word WZ7, as shown in FIG.9(a), is programmed for a logic "0" as its drain terminal is connectedwith the source terminal of connecting MOS Transistor 87 which is tiedto virtual ground line SP7.

Logic "1" in contrast therewith is probed in, in that the drain orrespectively source electrodes are connected to a common line,preferably, as can be ascertained from FIG. 9(a), to a gap lineSP0,SP2,SP4,SP6,SP8. Thereby, the transistors, such as the transistor71b of word WZ0 as shown in FIG. 9(a), are short circuited.

The connections of the transistors are thus initially determined withthe application of the metal mask. In the usual manner two (throughcontacting) metal masks are applied on the ROM. In should be understoodthat in this instance preferably the lower of the two metal masks,meaning the mask which is located closer to the transistors, is employedfor the short circuiting and the connection of the applicabletransistors. Inasmuch as the transistors are short circuited, this doesnot influence the operation of the metal mask which is employed for thecontacting. Since this metal mask is usually one of the uppermostlayers, for example the tenth of about 14 layers, the inventive ROM canbe pre-manufactured up to the ninth layer and then programmed andmanufactured in accordance with the application.

In FIG. 9(b) there is illustrated a usual programmed ROM. It can beascertained from FIG. 9(b) that the transistors, which are shortcircuited in FIG. 9(a), are in any event not produced in the diffusionmask. As shown in FIG. 9(b), the transistor 71c which is not presentcorresponds to a short circuited transistor 71b in the metal maskpursuant to the process described above.

Each of the algorithms, subroutines, manufacturer data, and dataconstants stored in ROM and utilized by the smart battery module forcalculating the battery capacity, etc. as mentioned above, will now beexplained in further detail below. Further details of the smart batteryalgorithm for reporting battery parameters to an external device isfound in applicant's co-pending patent application U.S. Ser. No.08/318,004 assigned to the assignee of the instant invention and thedisclosure of which is incorporated by reference herein.

As shown in FIG. 3, the battery operating system 10' will first performan initialization routine 100 that is initiated upon system power up,enabled by a power ON signal/reset impulse signal 11, or, enabled by awakeup from STANDBY signal 13 which is generated after themicroprocessor has determined that it should exit the standby mode. Asshown in FIGS. 2(b) and FIG. 10, the hybrid IC 32 is provided with apower-on reset circuit 85 which generates a reset impulse signal 11 toactivate the external crystal oscillator 36 and reset the system everytime the power supply voltage is applied to the ASIC. Specifically, thisreset impulse initiates the start of the external crystal oscillator 36to provide the precise triggering of the internal 450 kHz oscillator forproviding the time base for the hybrid IC components. The threshold ofthis circuit is between 1.2 V and 1.6 V depending upon the type oftransistors used in the circuit of FIG. 10.

More specifically, as illustrated in FIG. 10, the power-on reset circuit85 is provided with a transistor network comprising n- and p- channeltransistors that are tied to hybrid IC voltage supply V_(DD). WhenV_(DD) is sensed as dropping between 1.6 V to 2.0 V, or, in the case ofbattery short circuit 0.0 V, the transistors of circuit 85 generate aRAM memory de-latching signal 79 which turns off PMOS- transistor 85'and effectively de-latches RAM memory 65. As mentioned above, thevoltage on buffer capacitor C4 will keep RAM memory contents alive forperiod dependant upon RAM leakage current.

After a power on/reset signal 11 is received, or, after the sleep modeis exited, the system is placed in a standby mode 23 (FIG. 3) until itis triggered by trigger signal 17 generated by the external oscillator36 which provides the trigger for the system operations (capacitycalculation) every 500 msec, or, is awakened by a bus request signal 15as will be explained in further detail below. In the battery "standby"mode, the microprocessor is in an idle state until the operating cycletrigger 17 or external bus request signal 15 is received.

Initialization of Algorithm Variables

The initialization routine, which is described and shown (in FIG. 4) ofthe above-mentioned, co-pending patent application (USSN 08/318,004), isconducted at the virginal start of the system. The initializationroutine functions to clear all values to be stored in the system RAM andto assign all system default values. Preferably, many of the defaultvalues are constant values and are available in case of an emergencysituation wherein all RAM memory has been lost while the system was inthe STANDBY mode.

On power-on-reset as well as on a wakeup from the STANDBY mode of thechip (explained below), the program is started at an initial memoryaddress. A "checksum" test is conducted for checking whether the RAMmemory is valid whereby the capacity calculation is continued, or,whether the emergency mode (which uses ROM defaults) will be activated.Such an instance occurs when the chip switches into the STANDBY mode atlow battery voltage and then back into the ON mode when the battery isto be recharged.

If the "checksum" test fails, the μP will first clear all RAM bankscompletely, and, as consequence an internally generated CALIBRATED flagwill be cleared and the number of cells of the battery pack has to belearned, a process to be explained in greater detail below. Next, thedefault values (described below) are transferred from ROM to RAM. Toprevent exceptions in the capacity calculations to be describedhereinbelow, it is imperative that variables do not have undefinedvalues. This enables the algorithm to work in a catastrophic emergencymode in the event that all RAM memory has been lost. The default valuesof critical variables may then be substituted by correct values when thebattery system is reformatted at a battery service station using theoriginal manufacturer's data.

Included in the initialization routine will be an initialization ofFullChargeCapacity "full cap", RelativeStateOfCharge "SOC" and theRemainingCapacity "Itf" values, as well as state and other variables toensure a proper start of the capacity calculation. Then, the programresets all system timers such as the calculation of voltage, temperatureand selfdischarge timers before passing out of the initializationroutine. The capacity calculation will then initiated at each triggersignal 17 which is delivered every 500 msec by the external 32 kHzcrystal 36.

As explained above, the default values are necessary to ensure that upona power-on/ reset, the rechargeable battery capacity calculation(explained below) may be executed. The preferable nominal default valuesfor the critical parameters used for the capacity calculation algorithm151 and explained in detail in co-pending patent application (USSN08/318,004), are set forth as follows:

The DesignCapacity (theoretical or nominal capacity, hereinafter "nomcap") may range between 1700 maH to 2400 mAH, but, after a memory loss,the capacity calculation algorithm defaults to a preferred value of 2000mAh and the new capacity is relearned from that level; the default valueof the number of battery cells in the rechargeable battery pack is 6cells, however, this value may be changed depending upon the actualconfiguration of the battery pack; The AL REM CAP value represents theremaining capacity alarm triggering value and may range from 50 mAh to500 mAh. Preferably, AL REM CAP has a default value (AL REM CAP DEF) of200 mAh. An alarm condition exists when the remaining capacity is belowthis value (without taking into account the remaining capacity after EDVdue to current and temperature (i.e., the residual capacitycorrection)). The AL REM TIME value represents the estimated remainingtime at the present discharge rate and may range from 1.0 min. to 20min.. Preferably, AL REM TIME has a default value (AL REM TIME DEF) of10 minutes. This alarm condition exists while the calculated remainingtime to voltage breakdown (EDV), based on the minute average current(discussed below), is below the value of AL REM TIME and willautomatically be disabled when the battery is in the charging mode. TheAL DTEMP value represents the dT/dt alarm trigger condition and mayrange from 1° K./min. to 5° K./min.. Preferably, AL DTEMP has a defaultvalue (AL DTEMP DEF) of 2° K./minute. This alarm condition will existwhen the battery detects that the rate of its internal thermal rise(dT/dt) is greater than the AL DTEMP value. The AL HI TEMP valuerepresents the high temperature alarm trigger and may range from 310° K.to 345° K. Preferably, AL HI TEMP has a default value (AL HI TEMP DEF)of 328° K. Additionally, when the capacity calculation is started bypower-on-reset, the FullChargeCapacity, ("full cap" represents thelearned full charge capacity of the battery), will be initialized to theDesignCapacity (nom cap); the RemainingCapacity ("Itf") to 1/8 of thefull cap; and, the RelativeStateOfCharge ("soc") to 12.5% and thebattery state to capacity decreasing, and, specifically, toselfdischarging mode. The alarm timer N ALARM is set at 10 seconds andthis is the amount of time that an alarm condition will be broadcastbetween a host device and/or a battery charger as will be explained infurther detail below. It should be understood that these values aretypical values for a NiMH battery intended for use in a portablecomputer. Other types of battery chemistry, or portable devices, maycall for a different set of default values.

As shown in FIG. 3, after the system is initialized at step 100, thebattery will enter into a standby or maintenance mode 23 where it willeither awake upon a bus-request signal 15 or awake upon the externalcrystal trigger signal 17 every 500 msec. If the battery is awaked by abus request signal 15 as determined at step 21, then the battery willhandle the request by the handle request routine indicated at step 25where it will thereafter exit into the standby mode. The routine forhandling the requests 25 will be explained in further detail below.

If the system is triggered by the normal external crystal trigger signal17, and there are no bus requests, then the program disables the busrequests (approximately 37 msec before the trigger signal) and enablesthe A/D converter to begin the current, voltage, and temperaturemeasurements for the current operating cycle as shown at step 130 inFIG. 3. A "getvalues" status flag is then checked at step 139 todetermine whether A/D conversions of the raw current, voltage, andtemperature measurement values are to be performed. When this flag isset high (logic level=1), the raw current, voltage, and temperaturevalues of the rechargeable battery are obtained for the current triggercycle as shown at step 140. These raw A/D current, voltage andtemperature values are built into a special function register 61, asshown in FIG. 2(b), which is one of sixteen such registers provided inthe hybrid IC for subsequent storage in RAM as I, U, or T. If the"getvalues" flag is low (logic level=0), then no raw current, voltage,and temperature measurements will be obtained for the present cycle, andthe getvalues flag will toggle high (logic 1) at step 148 and theprocess will continue as shown in FIG. 3.

After new current, voltage, and temperature values are obtained (step140), the A/D measurements ready flag is set high (logic level=1) atstep 141, and a check is made at step 142 to determine whether thesystem is in a sample mode. Thus, at step 142, if the absolute value ofthe raw current, |I|, is determined to be below a threshold value of 10mA, then the battery system will operate at half the sample ratedepending upon the status of the sample mode flag. Thus, at step 143 inFIG. 3, a determination is made as to whether the sample mode flag islow (i.e., logic 0) or high (logic 1). If the sample mode flag is low,then the sample mode flag will toggle to a high level at step 144, andthe system is placed in a sample mode and the process proceeds at step149 to initiate the A/D conversion. If the sample mode flag is alreadyhigh (from the previous cycle), then the "getvalues" flag is set equalto zero at step 146, and the A/D converter is disabled at step 147. TheA/D conversion will not occur (to save power) and the algorithm proceedsto the capacity calculation (step 151). The "getvalues" flag is alwaysset low in the sample mode. The status of this flag ensures that an A/Dconversion will be skipped, and, as a consequence, no new valid datawill be available for the capacity calculation at step 150.

If the raw current, |I|, is determined at step 142 to be above the 10 mAthreshold, then the battery system will exit the sample mode (and thesample mode flag is set at logic 0) at step 145, and the A/D conversionof the raw current, voltage, and temperature values will be performed atstep 149. At step 150, a determination is made as to whether the A/Dmeasurement ready flag is high (logic 1) indicating that valid rawbattery parameter data has been received. If it is set high, then thecapacity calculation and attendant battery characteristic conversions(voltage, current, and temperature) will be performed. If the A/Dmeasurement ready flag is low (logic 0), then the capacity calculationis not performed in the current cycle, and the process proceeds to step158 where the bus request line for message transfer is enabled and thehybrid IC is placed in the sleep mode at step 23. The oscillator trigger17 continues to wake up the microprocessor every 500 msec, however, whenthe current is less than 10 mA, the A/D conversions and the capacitycalculations may be performed at an arbitrarily determined rate that isless frequent, for e.g., once every two or once every five seconds, toconserve power.

FIG. 8(a) illustrates the timing of the operating cycles under normalmode operating conditions 57a as compared when the system operates undersample mode conditions 57b explained below. As shown in FIG. 8(a) and,as mentioned above, the 32 kHz external crystal delivers the triggersignal 17 every 500 msec to initiate the raw voltage, current, andtemperature measurements, indicated as 158. Also initiated is thecapacity calculation 160 which utilizes the current, voltage, andtemperature measurements of the previous operating cycle. When the rawcurrent value obtained is determined to be below a threshold value of 10mA, the battery system will operate at half power, and no measurementswill be taken during the next 500 msec operating cycle as indicated as58b in FIG. 8(a).

However, measurements are taken one second later at the next operatingcycle as indicated as 58c. When the raw current value obtained isdetermined to be above a threshold value of 10 mA, the battery systemwill resume normal mode operation and during the next and subsequentoperating cycles, the capacity calculation and attendant batterycharacteristic measurements (voltage, current, and temperature) will betaken.

FIG. 8(b) illustrates the approximate time durations for the variousmeasurements. As a matter of design choice, the capacity calculation 160is performed in approximately 71 msec for each operating cycle.Thereafter, the alarm control subroutine 152 will be performed for aduration of approximately 29 msec and the charger control subroutine 154will be performed for a duration of approximately 2 msec if the smartbattery determines these operations are to be performed (see FIG. 3).The LED display routine 156 may be performed if it is requested by auser and the LED display control functions will take place forapproximately 23 msec as shown in FIG. 8(b). It should be understoodthat the aforementioned performance times for the various routines mayvary due to the accuracy of the internal 455 kHz oscillator, which mayvary with temperature. Each of the alarm control subroutine 152, chargercontrol subroutine 154 and LED display subroutine 156 will be explainedin further detail below.

Since the system management bus request line is inactive during thecapacity calculation, alarm control, charger control, and LED displayroutines, the microprocessor will be unable to receive requests from ahost device or battery charger as indicated for the time duration 158for each operating cycle shown in FIG. 8(a). Therefore, in eachoperating cycle, after the capacity calculation has been performed, theSystem management bus request line is enabled for the remaining time ofthe 500 ms cycle, as indicated in FIG. 8(b), so that it may respond to arequest from a host device or charger. Concurrently, the battery placesitself in the standby mode 23 whereupon it will be awaked for the nextcycle upon receipt of the system trigger signal 17, or, be awakened by abus request signal 15 as shown in FIG. 3. For a remaining 37 msec ofeach operating cycle, the bus request is again disabled as shown for thetime duration 158 prior to the next trigger signal 17. As mentionedabove, each system trigger signal 17 initiates the start of the internalclock 48 generating the 455 kHz signal for controlling the hybrid IC,microprocessor, A/D converter, etc.

Algorithm for Calculating Battery Capacity

The purpose of the capacity calculation is to continuously monitor thecapacity of the rechargeable battery in accordance to the formulaindicated by equation (1) as follows:

    CAP.sub.rem :=CAP.sub.rem +Σε.sub.c I.sub.c Δt.sub.c -ΣI.sub.d Δt.sub.d -ΣI.sub.s Δt.sub.s(1)

where CAP_(rem), also referred to hereinbelow as Itf, and indicates theremaining capacity in the battery at any given time expressed as mAh(milliamperehours); the Σε_(c) I_(c) Δt_(c) term represents the sum ofthe incremental increases in capacity as the battery is being chargedand takes into account a charge efficiency factor Δ_(c) accessedpreferably from look-up table values to be explained in further detailbelow with respect to FIG. 22(c), or, alternatively, may be obtainedfrom a response equation or by interpolating between several pointsstored in memory; a ΣI_(d) Δt_(d) term which represents the sum of thecontinuous decrease in battery capacity due to discharge associated withthe battery's usage; and a ΣI_(s) Δt_(s) term which represents thepredicted and measurable amount of self-discharge based uponself-discharging effects associated with the battery's chemistry and isa function of the battery state of charge and temperature. By knowingthe RemainingCapacity, Itf, at all times, it is possible to providebattery parameter information useable by a host computer (PC) or smartbattery charger to ensure safe and reliable battery use and to ensureprolonged battery life.

FIGS. 13(a) through 13(b) illustrate the capacity calculation routineperformed for the rechargeable battery pack at each trigger cycle. Inparallel, the current, voltage and temperature measurements are runningexcept when in the "sample" mode where these measurements are taken onceevery second. The sample mode is designed to save power consumption(i.e., the A/D conversions occur at half-frequency) and is switched onand off depending upon the amount of detected current. For example, whenthe current falls below 10 mA, the "sample" mode is enabled and lessfrequent measurements are made.

Normally the temperature, voltage and current are measured and updatedonce per cycle. The current is measured with an integrating method(explained in detail below), which recognizes its changes during theconversion time. All output values taken from SMBus requests andcapacity calculation are one period delayed. The A/D measurements arecontrolled by an on-chip oscillator at nominal 455 kHz and the operatingcycles--responsible for the integration time--by the precise 32 kHzoscillator. The lower accuracy of the absolute frequency value of theon-chip oscillator has no influence on the accuracy of the measurement.

As shown in FIG. 13(a), step 200, the first at step of the capacitycalculation, the IUT Calculation routine 200 is performed to firstconvert the raw analog/digital converter output data from register 61(FIG. 2(b)) into values having appropriate units useful for the capacitycalculation algorithm. Details of the IUT Calculation routine can befound in the above-mentioned, co-pending patent application (USSN08/318,004). Briefly, as illustrated in FIG. 12, at step 205, the rawA/D Current measurement, I raw, is scaled and converted to the actualcurrent value "I" in units of milliamps. Similarly, the raw A/D packvoltage measurement, U raw, is scaled and converted to the actualbattery pack voltage value "U" in units of millivolts. Next, asindicated at step 212, the μP checks the battery pack voltage "U" todetermine whether or not the individual cells of the battery pack havean output voltage less than 0.9 V. If a cell is detected as outputting avoltage less than 0.9 volts, then the battery pack is placed in a Sleepmode, as indicated at step 212'. As shown in FIG. 12, the followingactions take place when the battery state changes between an ON andSLEEP mode:

To save battery power and minimize current drain, the μP proceeds toswitch off: the A/D converter 60 at step 213 and 455 kHz on-chiposcillator at step 216. While in the sleep mode, the RAM memory contentsare kept alive by voltage from the battery with only memory leakagecurrent drain (which is dependent upon the amount of RAM). Additionally,the wake-up comparator circuit 80 (FIG. 11) is activated at step 217 andthen the μP sets a bit flag to tell the hardware to start a specialvoltage control logic to set itself for sleep, as indicated at step 218.

As shown at step 219 in FIG. 12, and, as illustrated in FIG. 11 thewake-up comparator circuit 80 is periodically activated by a triggersignal 77a derived from the external 32 KHz oscillator. At each period,the comparator is turned on to compare the ratio of pack voltage signal82 with the predetermined bandgap reference voltage signal 83 that issupplied from the bandgap reference circuit 62 (FIG. 4) and input to theinverting input of comparator 76. For a three cell battery pack, thebandgap reference voltage 83 is approximately 1.239 volts, but, thisvalue may be changed in accordance with the battery pack design. Whenthe ratio of pack voltage signal 82 V_(DD) of the ASIC has increasedabove reference voltage signal 83, then the comparator circuit willtoggle, as shown at step 220, to awake the μP and enable the A/Dconverter again to take measurements, as indicated at step 221. Thecapacity calculation will then continue with an initialization at step100.

A detailed schematic of the wake-up comparator circuit 80 is shown inFIG. 11. As shown in FIG. 11, the wake-up comparator circuit 80comprises a voltage divider comprising resistors R4 and R5 which aretied to the V_(DD) ASIC power supply to supply a ratio of V_(DD) packvoltage (signal 82) to a first non-inverting input of a comparator 76.As will be explained in further detail below, an NMOS (n-channel MOSFET)transistor switch 89b connected between resistor R5 and ground isnominally turned off in sleep mode to prevent battery current drain toground, but, is periodically turned on once every 500 milliseconds (30microseconds) by trigger signal 77a to enable the divided V_(DD) voltageto appear at the non-inverting input of the comparator 76.Simultaneously, the external oscillator trigger signal 77a, triggers thewake-up comparator circuit 80 by simultaneously turning on thetransistors 89a,b to enable comparator 76 operation. As shown in FIG.11, a low power current source 90 which is derived from the battery byexternal circuitry, turns on transistor switch 89a, to provide areference current to comparator 76. From this current source 90, theworking point of the comparator is fixed. Additionally, enable line 15ais tied to signal 77a to simultaneously enable the comparator to take ameasurement. Transistor switch 89b is turned on by signal 77b, which isoutput from inverter 72, to create a path to ground to enable V_(DD)voltage divider signal 82 to appear at the comparator input so that thecomparison may be made.

When the V_(DD) ratio is low (<0.9 V/cell) and the ratio of pack voltagesignal 82 is less than the A/D converter bandgap reference signal 83,then the comparator output signal 13 is low. When V_(DD) rises above thereference voltage 83, i.e., 3.33 Volts (1.11 volts per cell for athree-cell battery pack) the wake-up (comparator output) signal 13 goeshigh, thus, allowing normal sample mode operation to resume. As shown inFIG. 11, element 78 is a Schmitt trigger device which is a bistabledevice that is provided at the output of the comparator 76 to preventspurious oscillations appearing at the output of the comparator 76 thatmight be due to comparator switching characteristics and/or amplifiernoise.

Due to the low power consumption of the MOS circuitry implemented in thehybrid IC, the total current consumption of all operating componentswhile in the sleep mode is no greater than approximately 2.0 μamp(microamps).

Referring back to FIG. 12, as long as each cell is detected asoutputting a voltage greater than 0.9 volts, the capacity calculationcontinues, and, at step 215, the raw A/D pack current temperaturemeasurement, T raw, is converted to the actual battery pack temperaturein units of degrees Kelvin. This temperature value is additionallyscaled to take into account thermistor scaling values, (not shown), anda final current temperature value of "T" is obtained. At step 222, thecondition of the battery is checked to determine if an over temperaturecondition exists, where a temperature of 328° K. or greater is detected.When detected, a temperature alarm condition flag, HI TEMP ALARM, isset. If capacity is increasing and the over temperature condition existsthen a TERMINATE CHARGE ALARM flag will be set indicating that one ormore of the battery's charging parameters are out of range.

At this point, it should be mentioned that an end of charge conditionmay exist (if the capacity is increasing). This end of charge conditionmay be detected when the rate change in voltage or temperature takenbetween successive measurements is at a certain gradient. Thus, as shownin FIG. 12 at step 224, and described in detail (steps 240 through 249of FIG. 5(b)) in co-pending patent application (USSN 08/318,004), thechange in temperature dT/dt calculation is performed. Additionally, asshown in FIG. 12, a change in voltage dU/dt calculation is performed atstep 227.

The change in temperature (dT/dt) calculation is performed to evaluatethe difference dT between the current temperature value T and a previoustemperature value determined at a time 20 seconds previously, but mayrange anywhere from 10 to 120 seconds previous. After the dT calculationis performed, a determination is made as to whether the amount ofinternal temperature change exceeds the allowable rate, i.e., whetherthe AL DTEMP alarm condition exists, as shown at step 226 in FIG. 12. Atemperature change of approximately 2° K./min or greater indicates an ALDTEMP alarm condition and, when detected, an alarm condition flag, DTEMPALARM, is set.

The change in voltage (dU/dt) calculation is performed to evaluate thedifference dU between the current voltage value U and a previous voltagevalue determined at a time preferably 255 seconds previous.

After the dU calculation is performed, a determination is made at step260 as to whether the capacity is decreasing, and, as to whether thepresent voltage U is less than the end of discharge voltage (EDV) limit(typically 0.9 V/cell), indicating that an end of discharge conditionEOD U exists. Thus, the present voltage value U is compared to thepreset end of discharge voltage (Uempty) to determine if it is less thanthis voltage. If an End of Discharge condition for voltage exists, thenan EOD U flag is set at step 262 and a Terminate Discharge Alarm flag isset indicating that the battery has supplied all the charge, and is nownominally fully discharged. If an End of Discharge condition does notexist, then the EOD U flag and the Terminate Discharge Alarm flag arecleared at step 264. Additionally, at step 264, the capacity reset flagis disabled. The IUT Calculation procedure 200 is then exited and thecapacity calculation continues at step 165 in FIG. 13(a).

At step 165 of the capacity calculation routine 151 of FIG. 13(a), acalculation of the rolling minute average current is performed utilizingthe recent previous current (I) measurements. Rolling minute averagecurrent calculations are important for calculating battery conditionssuch as "average time to empty" which is based on the average currentdrain, and which might be requested by a host device, as will beexplained in greater detail below. Then, at step 170 of FIG. 13(a), adetermination is made as to whether the present current (I) value isless than or equal to the selfdischarge current I SELFD, which, in thepreferred embodiment, is 3.0 milliamps but may range anywhere from 2.0ma to 10.0 ma and represents the limit for a mode and battery staterecognition. If the present current (I) value is less than or equal tothe selfdischarge current then the state of the battery is determined tobe capacity decreasing without any external drain. Consequently, aselfdischarge flag bit is set at step 175. If the present current (I)value is greater than the selfdischarge current (3.0 mA), then thebattery selfdischarge flag bit is cleared at step 172. The batteryself-discharge current is always calculated regardless as to whether thebattery is in a capacity increasing or capacity decreasing state. Thedirection of current is established at step 178 in FIG. 13(a) todetermine the present state of the battery. If the current (I) isdetermined to be a positive value, then the state of the battery iscapacity increasing (hereinafter CI) and a capacity increasing flag isset at step 180. If the current is determined to be a negative value,then the state of the battery is capacity decreasing (hereinafter CD)and a capacity decreasing flag is set at step 182. If it is determinedthat the capacity is decreasing, then a determination is made at step184 as to whether the end of discharge voltage (plus hysteresis) EOD UHflag has been set.

For accurate battery parameter presentation and battery lifepredictions, it is important that the full battery capacity be resetafter an end of discharge voltage condition (battery nominally fullydischarged) has been detected. Even at a nominally discharged condition,some residual battery capacity remains and this is taken into accountinto the battery calculation, as will be explained below. Thus, adetermination is made at step 189 as to whether the capacity reset flaghas been set as a result of the EOD UH flag having been set indicatingthat the battery pack end of discharge voltage has been reached (asdetermined at step 184), or, as a result of the battery self dischargeflag having been set (as determined at step 175), or, if capacity isincreasing. If the capacity reset flag has been set, then, at step 190,the remaining capacity (Itf) at the EOD voltage condition is reset to apredicted Residual Capacity "pd" value obtained from look up tabledepicted in FIG. 22(a). Additionally, at step 190, the error register isreset to zero and the capacity reset flag is cleared. The program thenproceeds to the selfdischarge calculation and current integrationprocedures. If, at step 184, the EOD UH flag has been determined not tohave been set, or, if the capacity reset flag had not been set asdetermined at step 189, then the algorithm proceeds at step 192 in FIG.13(b).

As described in further detail (with reference to FIG. 6(b) ofco-pending patent application (USSN 08/318,004), and in view of step 192of FIG. 13(b), a state change determination is made for determiningwhether the state of the battery has changed, i.e., whether the batteryhas changed from a capacity increasing (CI) state to a capacitydecreasing (CD) state, or vice versa. This step is necessary to avoidthe instance of false battery cycle counting or the inaccurate learningof the full charge capacity due to current pulse sign changes or breaksof the current flow.

As indicated from steps 300 to 325 of FIG. 13(b), the selfdischargecalculation procedure is performed. Specifically, as described infurther detail (with reference to FIG. 6(b) of co-pending patentapplication (USSN 08/318,004), a 128 second timer for the selfdischargecalculation is first decremented. Preferably, steps 305-325 of theselfdischarge calculation are performed once every 128 seconds. If theself-discharge timer has not timed out, the program proceeds to step 400(indicated by broken lines) to perform the current integration procedure400, as shown in detail in FIG. 13(b) and explained in further detailbelow.

Selfdischarge calculation routine

Due to the electrochemical nature of batteries the selfdischargingcorrection of the remaining capacity has to be calculated all the time,independent from the existence of any charging or discharging currents.This is because there will always be a self-discharge current drainregardless of whether the battery is being charged or discharged and theamount current drain is a function of the battery charge andtemperature. Thus, as indicated as step 305 in FIG. 13(b), theselfdischarge rate "s" as a function of the relative state of charge"soc" and current temperature T is accessed via a look-up table, shownin FIG. 22(b) which shows a three-dimensional graphic representation ofself-discharge current (vertical axis) as a function of relative batterystate of charge and temperature. These look up factors "s" forselfdischarge give the predicted selfdischarge rate scaled by the design(nominal) capacity, and, as is shown in FIG. 22(b), the amount ofselfdischarge current, I_(s), generally increases with increasingtemperature and increased battery state of charge levels. For instance,at approximately 65° C. and a 95% relative state of charge, batteryselfdischarge current might total an amount of up to 30% of the fullbattery capacity per day. The selfdischarge values depicted in FIG.22(b) were empirically derived and will vary, depending upon the batterychemistry and battery architecture.

At step 310, a determination is made as to whether the state of thebattery is capacity increasing or capacity decreasing. If the battery isin a discharging state, as shown at step 315, the total amount ofcapacity decrease (current drained) since the last state change iscalculated and stored in a separate register. If the capacity isincreasing, then the program is directed to step 320, where the effectsof the selfdischarge rate is taken into account for the errorcalculation. Step 320 are also performed after the total amount ofcapacity decrease (current drained) since the last state change iscalculated at step 315. Then, at step 325, the actual capacity integral"Itf" is decremented by the selfdischarge rate "s", thus, providing theΣI_(s) Δt_(s) in equation (1) described above. Afterwards, theself-discharge procedure ends and the current integration routine 400 isperformed.

Battery Charge Integration Routine

When the battery is being charged, it is said to be in the CapacityIncreasing state (CI), else it is in the Capacity Decreasing state (CD).CD includes the standby mode of the battery, when no current flowsthrough the battery terminals. In the standby mode, only theselfdischarging rate reduces the capacity.

The battery current will be precisely integrated during both charge anddischarging states. The capacity integration itself is independent fromthe battery state, but, as will be hereinafter explained, look up tables(LUT) provide adjustment factors to enable more precise capacityadjustment. For instance, a first LUT (described below with respect toFIG. 22(c)) comprises current efficiency factors dependent upon thebattery relative state of charge, the C rate (current), and thetemperature; a second LUT comprising selfdischarging rates dependentupon relative state of charge and temperature; and, a third LUT withresidual capacity corrections dependent upon the discharging currentrate and temperature which give the fraction of the full capacity whichcan be extracted from the battery under relaxed conditions after thebattery has reached an end of discharge voltage condition at a givencurrent rate.

The flow diagram for the current integration process 400 is shown inFIG. 13(c). As shown in FIG. 13(c) the first step of the currentintegration process is to determine the magnitude of the relative stateof charge (soc). The soc is defined as the actual capacity expressed asa percentage of the full charge capacity (i.e., the capacity of thebattery when fully charged) and is used to estimate the amount of chargeremaining in the battery. Thus, as indicated at step 405, adetermination is made as to whether the remaining capacity is greaterthan zero (0). If the remaining capacity Itf is a negative number, thefull capacity is incorrect and must be learned and the soc value isclamped to zero (as indicated at step 412 in FIG. 13(c). Otherwise, thesoc calculation will take place at step 410. As previously described,until the full charge capacity of the battery is learned, the fullcharge capacity is initialized as the design (nominal) capacity.

Next, as indicated at step 415 in FIG. 13(c), the C rate is calculated.The C rate is defined as the rate in which it would take the energysource to drain in one hour and is measured at units of reciprocalhours. The C rate calculation in step 415 is based on the actual currentvalue (I) and the present full charge capacity value and is additionallyscaled. A determination is then made at step 418 as to whether thebattery is in a capacity increasing or capacity decreasing (discharging)state. If the capacity is increasing, then the battery is being chargedand the charge calculation must take into account a charge efficiencyfactor, made available in a LUT for charge efficiency, accessible by themicroprocessor, as graphically represented in FIG. 22(c). Thus, at step420 the charge efficiency factor dependent upon the charge current,relative state of charge (soc), and the temperature, is accessed. Forinstance, as shown in FIG. 22(c), when the battery is charged toapproximately 95% of full capacity, and the current is being charged ata 0.1 C rate at a temperature of 45° C., the charge efficiency factorε_(c) is found to be about 0.8. The charge efficiency factors areempirically derived and will vary depending upon the battery chemistryand battery architecture. The representations shown in FIG. 22(c) arefor a battery state of charge 95% and it is understood that chargeefficiency values will vary considerably depending upon (remainingcapacity) state of charge.

Finally, the increase in charge for the current time interval takinginto account the actual current and the charge efficiency factor iscalculated at step 435 to form the term ε_(c) I_(c) Δt_(c) in equation(1). This value will be used to increment the integration at step 445 aswill be explained below.

If at step 418 it is determined that the capacity is decreasing, theamount of discharge will be integrated for the current discharge cycleas indicated at step 422 in FIG. 13(c). It is next determined at step425 whether the self-discharge flag had been previously set (see step175, FIG. 13(a)) indicating that the battery discharge current is lessthan 3 mA, and that only the self-discharging processes need to beconsidered. If the self-discharge flag bit has not been set, a chargecalculation is made at step 440 to increment the integration. The finalintegration is accomplished at step 445 wherein the charge incrementcalculated at either step 435 or step 440 is added to the remainingcapacity Itf, and, as indicated in equation (1). Additionally, at step445, the charge is integrated for an error calculation and the runningtotal of the error is also calculated as will hereinafter be discussedin detail.

If it is determined at step 425 that the self-discharge flag has beenset (step 175), then the battery is self-discharging without anyexternal correct drain (step 175, FIG. 13(a)) and the residual capacityis calculated at steps 451 through 456. The first step of this routineis to determine the residual battery capacity value. This value, whichis dependent upon the current C rate and the temperature, is accessed atstep 451 by the microprocessor from the look-up table depicted in FIG.22(a). For instance, as shown in FIG. 22(a), at a temperature of -20° C.and a current drain of twice the C rate, (2C), it has been empiricallyderived that approximately 92% of the full battery capacity will remainwhen the end of discharge voltage is reached. When applying a light load(e.g., C/10 discharge rate) at a temperature of about 23° C., virtuallyno residual capacity will remain when end of discharge voltage isreached.

At step 455, a determination is made as to whether the C rate is greaterthan a high discharge threshold rate (preferably of mAh) and whether theEnd of Discharge flag (see step 262, FIG. 12) had been set. If not, thenthe capacity calculation at steps 440 and 445 is performed as describedabove. If the current discharge rate is higher than the high dischargethreshold rate, then all of the capacity resets are disabled, asindicated at step 456, and the integration procedure continues at step440.

During the operational state of the battery, whether the batterycapacity is increasing (CI) or decreasing (CD), the end of chargeconditions (EOC) and end of discharge (EOD) conditions, respectively,have to be observed. Therefore, the capacity calculation routineillustrated in FIGS. 13(a) and 13(b) continues by making a determinationas to whether the battery is in a capacity increasing or capacitydecreasing (resting or discharging) state, as indicated at step 198 inFIG. 13(b). If the capacity is increasing, then the routine fordetermining whether an End Condition CI has been met as indicated atstep 500. If the capacity is decreasing, then the routine fordetermining whether an End Condition CD has been met as indicated atstep 600.

Observation Routine for Capacity Increasing End Conditions

The microprocessor of the hybrid IC calculates a charge termination byone of three methods: a negative voltage slope greater than 10mV/cell/min+/-5 m V/cell/min at a full charge voltage; a A.sup.ΔT/.sub.Δt that exceeds 0.9° /min+/-0.2° /min, or a preferred calculatedcharge of 120% of full charge capacity (but may range from 100% to 150%of CAP_(FC). The routine for determining if one of the EOC triggerconditions has been met is illustrated in the flow diagrams of FIGS.14(a)-14(d).

If it is determined that the capacity is increasing, then the first step505 of the EOC (CI state) observation process 500 illustrated in FIG.14(a), is a determination of whether the battery's relative state ofcharge (soc) value is greater than 20% of the battery's full chargecapacity value. If the battery has attained that level of capacity, thenthe fully discharged status flag is cleared at step 507. As will beexplained below, the fully discharged status flag is set when it isdetermined that the battery has supplied all the charge it can withoutbeing damaged. Until the battery reaches that capacity level, the FULLYDISCHARGED status flag will remain set. Next, as indicated at step 510,the first EOC trigger detection method is performed. This first methodis a determination as to whether the dT/dt trigger enable condition hasbeen met, and, whether the slope of the temperature increase dT isgreater than or equal to a threshold limit indicating an EOC condition.In the preferred embodiment, the dT/dt trigger enable condition issatisfied whenever the relative state of charge (soc) is above a 50%threshold limit, and, an end of charge condition is detected when theslope of the temperature increase becomes greater than a threshold ofabout 0.9° C./min. It should be mentioned that the slope of thetemperature may trigger EOC when it is detected within the range from0.5° C./min to 12° C./min. If either of these conditions are notsatisfied, then a second method of detecting an EOC condition, namely, adetection of whether the slope of the voltage change, dU/dt, becomesnegative wherein the value of dU/dt must have a minimum amount and thecharging current rate (C rate) must be greater than a certain value, isperformed at step 540 as will be explained in further detail below. Ifthe dT/dt trigger enable condition has been met and the slope of thetemperature increase dT is greater than or equal to the EOC thresholdlimit, then a determination as to whether the EOC flag has been set ismade at step 512. When the EOC flag has not been set, then the number ofcells in the battery pack will have to be learned--a process indicatedas element 700 in FIG. 14(b) to be described below. Whether or not thenumber of cells in the battery pack is learned (as will be explainedbelow), at step 700, then step 570 is performed wherein: a) the EOCstatus flag is set; b) the remaining capacity is set equal to 95% of thefull charge capacity; c) the error registers are cleared; d) theoverflow flag for the uncertainty calculation is cleared; and, e) thefully charged status flag is set indicating that the battery has reacheda charge termination point. Finally, the algorithm proceeds to step 575,shown in FIG. 14(c), where the terminate charge alarm flag is set.

If the dT/dt trigger enable condition has been met, the slope of thetemperature increase dT is greater than or equal to the EOC thresholdlimit, and the EOC flag has been set (step 512), then a determination ismade at step 514 as to whether the remaining capacity (Itf) is greaterthan or equal to the full charge capacity. If this condition issatisfied, then the remaining capacity is set to the full chargecapacity as indicated at step 520. Additionally, at step 520, the errorregisters are cleared and the overflow flag for the uncertaintycalculation is cleared. If the remaining capacity (Itf) is not greaterthan or equal to the full charge capacity (step 514) then the algorithmproceeds to step 575, shown in FIG. 14(c), where the terminate chargealarm flag is set. In the preferred embodiment, the terminate chargealarm flag must be set when the battery detects EOC on any of the EOCtrigger conditions or when an over temperature condition exists, i.e.,if T≧AL HI TEMP (step 222, FIG. 12). As explained above, the terminatecharge alarm flag may already be set by the 95% full-trigger, which isinitiated when the first temperature slope trigger condition issatisfied at step 510.

After the remaining capacity is set to the full charge capacity at step520, the algorithm proceeds at step 530 to determine whether the batterycharger is still on. This is accomplished by checking for a positivecharge increase obtained during the charge integration process (see step435, FIG. 13(c)). If the charger is still on, then it is known that thecharger is continuing to overcharge the battery, and the algorithm mustkeep track of the amount of battery overcharge. Thus, at step 532 inFIG. 14(a), the total amount of overcharge is calculated by adding thecharge increase to the overcharge registers (not shown). It should bementioned that the overcharge register is never reset, so that the totalamount of overcharging since the system start-up is retained. Whether ornot the battery charger is still on, the algorithm proceeds to step 535where the overcharging alarm status flag is set indicating that thebattery is being charged beyond an EOC indication. Finally, thealgorithm proceeds to step 575, shown in FIG. 14(c), where the terminatecharge alarm flag is set.

As mentioned above with respect to step 510, if either the dT/dt triggerenable condition has not been met, or, the slope of the temperatureincrease dT is not greater than or equal to the EOC threshold limit,then a second method of detecting an EOC condition is performed at step540 shown in FIG. 14(c). At step 540, a determination is made as towhether: a) the charge is constant current, i.e., whether the differencebetween the current value and the average current value for one (1)minute is preferably less than 50 milliamps; b) whether the dU/dtvoltage change is negative and is greater than a threshold amount ofpreferably 12 mV/m; and, c) whether the charge current is greater than apredetermined rate, preferably, a rate of C/10. If either of the secondmethod EOC trigger conditions are not satisfied, then a third method ofdetecting an EOC condition, namely, a detection of whether the relativestate of charge (soc) is above 120% and the current rate is between C/50and C/5 is performed at step 545. It should be mentioned that the EOCcondition may be triggered when the relative state of charge (soc) isdetected within the range of 100% to 160%. If all of the second methodEOC trigger conditions are satisfied, or, if all of the third method EOCtrigger conditions are satisfied, then a determination as to whether theEOC flag has been set, is made at step 550 in FIG. 14(c). If either thesecond method EOC trigger conditions or third method EOC triggerconditions are satisfied, and the EOC flag has been set (step 550), thenthe fully charged status flag is set at step 555 indicating that thebattery has reached a charge termination point. Afterwards, the processproceeds at step 520, FIG. 14(a), by clamping the remaining capacityvalue to the full charge capacity value as described above. If the EOCflag has not been set, then the number of cells might have to belearned--a process indicated as element 700 to be described below. Whenthe process of learning the amount of cells in the battery is complete,then the EOC status flag will be set at step 551, and the fully chargedstatus flag is set at step 555 indicating that the battery has reached acharge termination point and the algorithm continues at step 520described above. If all three EOC trigger conditions are not satisfied,then the EOC detection procedure 500 is exited and the capacitycalculation (FIG. 6(b)) continues.

Alternately, a -dU trigger condition will be reached when it isdetermined that the battery capacity is increasing, dU>DU MIN, where DUMIN is a predetermined value equal to the number of battery pack cellsmultiplied by 10 mV, and the current is determined to be constant andthe charge rate is higher than 0.3 C. The charge current is consideredconstant if |I-I avg |<50 mA and |I-I⁻¹ |<50 mA where I⁻¹ was theprevious value of the current measurement. The constancy of the batterycharging may be calculated in addition to, or, in place of steps 250 etseq. of the IUT calculation routine FIG. 5(b), where the method ofcalculating -dU may be accomplished without time dependency.

Learn Number of Cells Routine

As described above, an emergency power-down condition may occur whereinall RAM contents are lost. In such a situation, it may be necessary torelearn the number of cells in the battery pack. Rather than burning inthe number of cells for a particular battery module in the ASIC ROM, thenumber of cells may be learned to enable the ASIC to be configured withother battery packs having a different number of cells. The relearningof the number of cells is indicated by a bit (CALIBRATED bit) in the ALSTATUS register, which will indicate whether the number of battery cellshas to be relearned. In the preferred embodiment, it is easilyaccomplished by utilizing the voltage measured at the battery packterminals after an EOC condition, described above, is met.

The first step 705 in the learn number of cells procedure 700 shown inFIG. 14(d), is to determine whether the battery pack is uncalibrated,i.e., whether the CALIBRATED bit in the AL STATUS register indicatesthat the number of cells should be learned. If so, it is determined atstep 710 whether the converted voltage value, U (mV), measured at step210, FIG. 5(a) during the IUT calculation procedure, is greater than 11volts. If so, then it is concluded that the battery pack has nine (9)cells and the number of cells is set at nine in step 720. If themeasured voltage value, U, is not greater than 11 volts, then adetermination is made at step 715 as to whether the voltage is greaterthan 7.5 volts. If so, then it is concluded that the battery pack hassix (6) cells and the number of cells is set at six in step 725. If themeasured voltage value, U, is not greater than 7.5 volts, then it isconcluded that the battery pack has four (4) cells and the number ofcells is set at four in step 730. After the number of cells isdetermined, the EOD cutoff voltage, Uempty, is set equal to the numberof cells multiplied by the operating battery voltage of 1.02 Volts inthe preferred embodiment as indicated at step 740 in FIG. 14(d).

Observation Routine for Capacity Decreasing End Conditions

As previously mentioned, the capacity calculation routine 151 at step198 makes a determination as to whether the battery is in a capacityincreasing or capacity decreasing (resting or discharging) state. If itis determined that the capacity is decreasing, then the first step 605of the EOD (CD state) observation process 600 illustrated in FIGS. 15(a)and 15(b), is a determination of whether the present voltage measurement(U) is greater than the end of discharge voltage (EDV) and anyhysteresis. When the EDV voltage is reached, it is an indication thatdischarging should be stopped to save the battery from damage.Typically, the EDV is 1.02 V/cell. If the voltage obtained is greaterthan the EDV voltage, then a flag indicating that the voltage is greaterthan the EDV voltage plus hysteresis is set at step 610. If the voltageis not greater than the EDV voltage plus hysteresis, then the flag iscleared at step 612. Additionally, as indicated at step 613, since thecapacity is decreasing, the Terminate Charge Alarm and Over ChargingAlarm flags are cleared.

A determination as to the value of the remaining capacity (Itf) is madeat step 615, where it is determined whether the remaining capacity isless than the calculated error (i.e., the uncertainty capacity). If theremaining capacity is less than the calculated error, then this is anindication that the battery pack has no more capacity and is fullydischarged. Consequently, the FULLY DISCHARGED status flag is set atstep 618 and the process continues at step 619. If there is remainingcapacity, then the FULLY DISCHARGED flag is not set, and the processcontinues at step 619 where a determination of the relative state ofcharge is made. If the relative state of charge (soc) has dropped belowsome hysteresis value, preferably, about 80% of the full chargecapacity, then the FULLY CHARGED status flag is cleared, as indicated atstep 620. Whether the FULLY CHARGED status flag is cleared or not, theprocess continues at steps 625 and 630, where the cycle count number isupdated. At step 625, a determination is made as to whether a cyclecount flag is cleared, and, whether the capacity has decreased by 15% ofnominal capacity. If these two events of step 625 have occurred, thenthe cycle count register, containing a value of the number of times thebattery has been charged or discharged (not shown), will be incrementedat step 630 and the cycle count flag will be set. It should beunderstood that in the preferred embodiment, the cycle count will beincremented whether or not the battery has been fully or partiallycharged. Whether the cycle count flag is incremented or not, the processcontinues at step 640, where a check is made as to whether the EOD flagis set, and, whether the reset flag is clear. If either the EOD flag isnot set, or, the reset flag is not clear, then the end conditionobservation routine 600 is exited. If the EOD flag is set, and, thereset flag is clear, then a determination is made at step 645 as towhether the EOC (end of charge) flag has been set and whether the errorvalue (uncertainty capacity) is less than 8% of nominal capacity. Ifthese conditions are satisfied then the full charge capacity value islearned at step 650. Specifically, whenever the battery has performed afull cycle reaching an EOC trigger point and the EOD point and theuncertainty capacity is below 8% of the nominal capacity, the fullcharge capacity is reset at step 650 with the formula:

    full cap=full cap+full cap* pd/256 -Itf

where "pd" is the predicted residual capacity correction value accessedfrom the look-up table of FIG. 22(a) and is dependent upon thedischarging current rate and temperature. The divisor 256 provides foran integer scaling of pd. The meaning of the formula is to exchange theremaining capacity (Itf) by the residual capacity from the LUT table,which contains fractions of the full charge capacity (Note: the residualcapacity obtained is calculated from step 451 of the charge integrationprocess of FIG. 13(c)). If the EOD point is reached with less capacityoutput as in the former cycle, the amount of Itf (remaining capacity)will be higher at EDV (less discharged capacity compared with theaccumulated charged capacity). The full charge capacity will be reducedby the difference of Itf compared with the former cycle so that theageing of the battery is taken into account by this learning step. Ifthe battery is used in several partial charge/discharge cycles withoutreaching an EOC or EOD point, the error of the calculation canaccumulate to a heavy difference between the real capacity and thecalculated remaining capacity (Itf). The algorithm (MaxErroro()), to beexplained in detail below, calculates the maximum possible error(uncertainty) during its operation as precise as the capacityintegration itself on the base of a percentile error for each operatingmode. The uncertainty is reset to zero at each EOC and EOD point. Anuncertainty of above 8% disables the full capacity reset. Additionally,when the conditions at step 650 are satisfied, the EOC flag is clearedindicating that the full charge capacity has been reset. After the fullcharge capacity is reset (step 650), or, if it is determined that theuncertainty error is greater than the prespecified value of 8%, or, theEOC flag is not set, then the algorithm continues at step 655.

At step 655, a determination is made as to whether the C rate at the EDV(end of discharge voltage) trigger is equal to zero, or, whether thepresent C rate is less than the C rate at the EDV trigger, and, whetherthe capacity reset is not disabled. If either of these conditions aresatisfied, the present current at the EOD trigger is set equal to thepresent C rate, the delayed capacity reset value is set equal to thepresent residual capacity value, and, the flags to delay capacity resetafter EOD are set at step 660. Else, if both of the conditions of step655 are not met, then the end conditions observation routine 600 isexited. As indicated in FIG. 13(b) of the capacity calculation routine151, if the EOC and EOD triggering has not occurred, then the capacitycalculation is exited.

System Management Bus and Bus Interface

As described above, and as shown in FIGS. 2(a) and 2(b), a modifiedPhillips I² C bus interface is used by the battery module 28 tocommunicate within a configuration comprising the ASIC 32 and thebattery 10, a host computer 16, and a smart charger 22. As mentionedpreviously, requests are either from the host computer to the battery,from the charger to the battery, or, from the battery to either the hostor charger. An example of a typical communication between the batteryand the charger may be to switch the charger on and off, or, to demand acertain charging rate. The host computer may request information of thebattery such as the battery state, or, the battery alarm conditions suchas minimal capacity, or, overtemperature. The bus interface controlcircuit 75 controls all requests and alarm conditions via two serialports SMBCLK and SMBDATA over the system management bus.

When the battery 10 needs to inform the host of an alarm condition or toinform the battery charger about its desired charging voltage orcurrent, the battery acts as a bus master with write functioncapabilities. The battery will function to: evaluate the request fromthe μP 50; check if the system management bus is free; generates a startbit and sends the address of the battery charger or host; checks whetherthe ACK-bit has been sent from the charger or host and gives a messageto the μP; sends the data supplied from the μP on the bus and checks forACK bit; generates a stop-bit at the end of the transfer.

When the battery 10 is requested by the host to provide it withinformation to be explained below, the battery acts as a bus slave withread and write capabilities. For instance, during the steady-stateoperation, the host might request some information from the battery andwill formulate a request. FIG. 16 illustrates the software algorithmcompatible with the system management bus interface protocol forproviding communication between an external device (host PC or batterycharger), and the battery, which acts as a slave thereto.

Specifically, the first step 750 in FIG. 16, is to decode the commandcode that has been sent by the external device. Illustrative commandcodes are discussed hereinbelow, and each typically requires two bytesof data to be transmitted which is indicated as the variable "count".The next step, indicated as step 752, is to determine whether thecommand code sent is a valid, recognizable command word. If not, aunsupported command bit is set at step 755 and the transmission will beterminated as indicated at step 758a in FIG. 16.

If the command is supported, the battery will perform an internal checkto determine if an error has occurred at step 759. If an internal erroris found, then the algorithm will enter a timer loop which will keepchecking the internal flag until an error is confirmed or the timer (notshown) times out. This is indicated at step 761. If a correct value isfound at step 759, then the algorithm will continue at step 764 todetermine if the decoded command code calls for a read or writefunction. If the timer has timed out, or, an error is confirmed at step761, then an unknown error flag is set at step 763 and the softwaretransmission is terminated at step 758b.

When functioning as a slave, the battery will perform either read orwrite functions. At step 764, a determination is made as to whether thecommand code input (step 750) is a read or write command. If it is aread command, a determination is made at step 765 as to whether thebattery is to perform a calculation as requested by the external deviceand return a value to be read by the external device. Examples ofcalculations made by the battery in response to a query (for e.g.,AvgTimeToEmpty()) from a host device are described in greater detailbelow. The battery μP will proceed to perform the calculations at step768 and will return a data value to a specified address location asindicated by the read block routine at step 800 and explained in detailbelow. If it is determined at step 765 that a calculation is not to beperformed, (for e.g., only a voltage value is requested) then thealgorithm will proceed directly to the read block routine 800 as shownin FIG. 16.

If, at step 764, it is determined that a write function is to beperformed wherein a data value is to be written to the battery addresslocation from an external device, (for e.g., the AL REM TIME thresholdvalue), then a write block authorization check must be performed todetermine if the external device may perform the write function. This isindicated at step 771 where a password is checked for validity. If thepassword checked is not an authorized password, then access will bedenied as indicated at step 774, and the external device will not beable to perform the write function and will terminate the softwaretransmission at step 758b. If the external device is authorized to writedata to a battery address, then the device will write a data value topre-specified address locations, as indicated by the write block routineat step 775 to be explained in detail below.

Host to Smart Battery Communication

A host to smart battery communication transfers data from the battery toeither a user (of a host PC, for e.g.), or, the power management systemof an external device. A user can get either factual data, such asbattery characteristic data, (Voltage(), Temperature(), charge/dischargeCurrent(), AverageCurrent() etc.), or, predictive (calculated) data suchas the battery's remaining life at the present rate of drain, or, howlong it will take to charge the battery. It should be mentioned that areal load, e.g., a host PC monitor, has a constant power consumption.When remaining time values described below are calculated (using theassumption that the currents are constant), errors and inaccuracies mayoccur. Thus, it should be considered to assume a constant powerconsumption of the load when calculating the remaining time and othervariables. Thus, in the following calculations such asRemainingCapacityAlarm(), AtRate(), RemainingCapacity(),FullChargeCapacity(), and DesignCapacity() . . . , average power valuesmay be utilized as an alternative to average current values.

The following control commands are representative of battery suppliedinformation when queried by a host device or host PC:

The RemainingCapacity() function returns the battery's remainingcapacity and is a numeric indication of remaining charge. Depending uponthe capacity mode bit, the RemainingCapacity() function will return avalue in mAh or 10 mWh. The value returned is calculated as follows:

    Itf mAh!-Itf err mAh!

where the uncertainty error Itf err is the subtracted value and theoutput value is set at 0 if (|Itf |<|Itf err|).

The RemainingCapacityAlarm() function sets or retrieves the low capacitythreshold value AL REM CAP (described above) for the low capacity alarmvalue stored in RAM. When the RemainingCapacity() falls below the AL REMCAP value, the battery sends Alarm Warning() messages to the host withthe REMAINING CAPACITY ALARM bit set. At manufacture, the AL REM CAPvalue is set to 10% of design capacity and will remain unchanged untilaltered by the RemainingCapacityAlarm() function. This function is usedby any host system that desires to know how much power it will requireto save its operating state. It enables the host system to more finelycontrol the point at which the host will transfer to a low power mode.

The RemainingTimeAlarm() function sets or retrieves the AL REM TIMEalarm value. When the estimated remaining time at the present dischargerate as calculated by the AverageTimeToEmpty() function falls below theAL REM TIME value, the battery sends Alarm Warning() messages to thehost with the REMAINING TIME ALARM bit set. An AL REM TIME value of zero(0) effectively disables this alarm and the value is initialized to 10minutes at time of manufacture. The FullChargeCapacity() functionreturns the predicted or learned battery pack capacity when it is fullycharged and is expressed either in current (mAh or 10mWh) depending uponthe setting of the CAPACITY MODE bit (discussed below). TheDesignCapacity() returns the theoretical capacity of a new battery packwhich when compared with the value returned by the FullChargeCapacity(),will provide an indication of the battery wear. This information isuseful by a host device or host PC to adjust its power managementpolicy.

The AtRate() function is the first half of a two-function call-set usedto set the AtRate value used in calculations based on capacity made bythe AtRateTimeToFull(), AtRateTimeToEmpty(), and, AtRateOK() functions.

When the AtRate value is positive, the AtRateTimeToFull() functionreturns the predicted time, preferably in minutes, to fully charge thebattery at the AtRate value of charge (value is in mA or 10 mW). Thecalculation formula is governed by equation (2): ##EQU2## where "time"is the returned value in minutes.

The AverageTimeToFull() function returns the predicted remaining time inminutes until the battery is full if a current like the last minuterolling average, I avg, value is continued. The calculation formula isgoverned by equation (3): ##EQU3## where "time" is the returned value inminutes.

When the AtRate value is negative, the AtRateTimeToEmpty() functionreturns the predicted operating time, preferably in minutes, at theAtRate value of battery discharge, until the battery will be exhausted(EDV condition). The calculation formula is governed by equation (4):##EQU4## where "time" is the returned value in minutes, |AT RATE|and pdat rate values are calculated by the AtRate() function where pd at raterepresents the remaining capacity (fraction of full capacity) and isdivided by the value of 256 to scale that value to a fraction. Itf erris the uncertainty error as explained below.

When the AtRate value is negative, the AtRateOK() function returns aBoolean value that predicts the battery's ability to supply theAtRatevalue of additional discharge energy for 10 seconds, i.e., if thebattery can safely supply enough energy for an additional load after thehost PC sets the AtRate value.

The RunTimeToEmpty() function returns the predicted remaining batterylife at the present rate of discharge (minutes) and is calculated basedon either current or power depending upon the setting of the CAPACITYMODE bit (discussed below). The value returned by this function can usedby the host PC or device power management system to get informationabout the relative gain or loss in remaining battery life in response toa change in power policy. The calculation formula is governed byequation (5): ##EQU5## where "time" is the returned value in minutes andtakes into account the remaining capacity in the battery after EDV whichcan be get out only by reduction of the load; |I| is the current,pd:=pd(C rate(|I|, T) and is calculated in the capacity calculationalgorithm pd represents the remaining capacity (fraction of fullcapacity). This value is divided by 256 to obtain a fraction. Itf err isthe uncertainty error as explained below.

The AverageTimeToEmpty() function returns a one-minute rolling averageof the predicted remaining battery life (in minutes) and is calculatedbased on either current or power. This function provides an averaging ofthe instantaneous estimations, thereby ensuring a more stable display ofstate-of-charge information. The calculation formula is governed byequation (6): ##EQU6## where "time" is the returned value in minutes, Iavg is updated every 0.5 sec, pd avg:=pd(C rate(I avg), T) and iscalculated in the alarm control routine one cycle before and representsthe predicted residual capacity (fraction of full capacity). This valueis divided by 256 to obtain a scale fraction. Itf err is the uncertaintyerror as explained below.

FIG. 23 illustrates two voltage versus time graphs, a and b, comparingcalculated battery capacity characteristics at various dischargingcurrent rates for a six (6) cell battery pack. As shown in FIG. 23,graph a, the voltage will rapidly decrease to an end of dischargecondition in a short amount of time when a load amounting to a dischargerate of 2C and yielding approximately 1.554 Ah (amperehours) is appliedto the battery. When the load is significantly decreased to a C/5discharge rate, the battery pack voltage will rise to extend the life ofthe battery for an amount of time to yield another 0.816 Ah. Graph b,which is of a different time scale than graph a, shows that discharge atthe C rate will yield approximately 2.307 Ah. When that load islightened to one half the C rate, the battery voltage will increaseslightly and the battery life can be predicted to extend for an amountof time to yield another 0.078 Ah until end of discharge voltage isreached.

As discussed above, certain calculations are dependent upon the value ofthe uncertainty capacity, i.e., the maximum possible error obtainedduring the capacity calculations. The MaxError() function returns theactual uncertainty in the capacity calculation in percentage. AMaxError() output of 20% means that the real value may be between 10%below and 10% above the internally calculated capacity. Most of thecalculations in the system management bus interface already subtract theuncertainty error, so that the error will be -0/+ MaxError()%. Theuncertainty is set to zero on EOC and EOD conditions by the capacityalgorithm as explained above. The calculations performed are as follows:##EQU7## where Itf err C D is the always positive accumulated chargeduring the charging and discharging mode; Itf err S is the accumulatedcharge of the self discharging process. Because of the permanentpresence of selfdischarging, even while charging, this accumulation isdone all the time using the LUT dependency from relative state of charge(soc) and temperature. Both accumulators are reset to zero at EOC andEOD condition. EPS is the error fraction of the capacitycalculation--especially from the LUT and from A/D measurement--whilecharging or discharging, with the scaling factor 256 applied. EPS S isthe error for selfdischarge-charge integration as fraction. Theuncertainty will grow undesirable if the battery will not be fully ordischarged over several cycles and the learn mode of the full capacitywill be disabled.

The CycleCount() function returns the number of charge/discharge cyclesthe battery has experienced. The cycles count on each charge decreasewith the amount of 15% of the design capacity after the last recharging,which needs not to be a full charging.

Other registers contained in the DBOS memory scheme is the BatteryMode()register which is used to select the battery's various operationalmodes. For instance, the BatteryMode() register is defined as containinga CAPACITY MODE bit which is set to specify whether capacity informationis to be broadcast in units of mAh or mWh (milliwatthours). This bitallows power management systems to best match their electricalcharacteristics with those reported by the battery. For example, aswitching power supply is best represented by a constant power model,whereas a linear supply is better represented by a constant currentmodel. Additionally, the BatteryMode() register contains a CHARGER MODEbit which is set to specify whether charging voltage and chargingcurrent values are to be broadcast to the smart battery charger 22(FIG. 1) when the smart battery requires charging. This bit allows ahost PC or battery charger to override the smart battery's desiredcharging parameters by disabling the smart battery's broadcast of thecharging current and charging voltage.

Another function calculated on the basis of capacity is theBatteryStatus() function which is used by the power management system ofa host device or PC to get alarm and status bits, as well as error codesfrom the battery status register. This function returns the battery'sstatus word flags including alarm warning bits such as OVER CHARGEDALARM, TERMINATE CHARGE ALARM, DTEMP ALARM, OVER TEMP ALARM, TERMINATEDISCHARGE ALARM, REMAINING CAPACITY ALARM, and, REMAINING TIME ALARM andstatus bits including INITIALIZED, DISCHARGING, FULLY CHARGED, and,FULLY DISCHARGED.

Ancillary functions that the battery 10 is capable of performinginclude: the SpecificationInfo() for providing the version number of thesmart battery specification the battery pack supports; theManufactureDate() for providing a system with information that can beused to uniquely identify a particular battery; the Serial Number(),which provides information for identifying a particular battery; theManufacturerName() function returns the name of the smart battery'smanufacturer; the DeviceName() function returns a character string thatcontains the battery's name; the DeviceChemistry() returns a characterstring that contains the battery's chemistry; the ManufacturerData()function which allows access to the manufacturer data (e.g., lot codes,number of deep cycles, discharge patterns, deepest discharge, etc.,contained in the battery.

Write Block Routine

As mentioned above, the battery may receive data from an external deviceto be used in a control command calculation, or, as an alarm thresholdvalue. The write block 775 illustrated in FIG. 17, controls thistransfer of data to the battery. First, at step 776, a determination ismade as to whether the data value to be read from the external hostdevice is greater than two bytes long. In the preferred embodiment, mostcontrol commands will write a data value to the battery that is twobytes long. If the data is longer than two bytes, i.e., if count >2,then the variable "w" is set equal to the number of address locationsallocated for and corresponding to length of data in number of bytes atstep 778. Then, at step 780, a determination is made as to whether thepreviously determined count value has been set equal to the addresslocations allocated. If this is not the case, then an error flag is setat step 790 indicating that an inordinate amount of data is to be sent,or, that there is not enough locations allocated for receiving the data.If the previously determined count value "count" has been set equal tothe number of address locations allocated, then the program enters aloop indicated as steps 781, 783 and 785 wherein each byte of data issequentially written to the I² C bus to the battery address locationAdr! (step 783). After each byte is sent, the count of the number ofbytes is decremented and the address location for the next sequentialdata byte to be written is incremented. Until count =0, indicating thatthe last byte of data has been transmitted to the battery as shown atstep 785, the loop will continue and enter at step 781 to determine ifthe battery has read each data byte (RDVAL =1) sent by the externaldevice and indicating that the data byte has been successfullytransmitted. If the read acknowledge flag has been received after eachbyte transfer, the loop continues at step 783 until the last data byteis sent. If the read acknowledge flag has not been received, then anerror may have occurred and the program proceeds to step 782 where adetermination is made as to whether a bus error or timeout has occurred.If none of these instances has occurred, then the program will proceedto step 787 to determine if the bus master has terminated thetransmission. If the bus master has terminated the transmission, then anerror flag is set at step 790 indicating that an inordinate amount ofdata is being transmitted and the transmission will be terminated atstep 795. If the bus master has not terminated the transmission, thenthe system will continue to look for the RDVAL flag until an internalhandshake timer (not shown) times out (step 782) and an unknown errorflag is set and the transmission will be terminated, as shown at steps792 and 795. In view of FIG. 17, it is understood that in some cases, afixed two-byte data word is to be read, as indicated at step 776, andthe algorithm will proceed directly to step 783 where the first databyte is read by the battery at the first battery address location.

After the last data byte has been received, as indicated at step 786, adetermination is made as to whether the stop bit flag has been receivedfrom the modified I² C bus master indicating the end of bus control dueto the fact that the external device will not be sending any more data.If the stop bit is received the write block routine is exited. If thestop bit has not been received, then an error may have occurred and theprogram proceeds to step 788 where a determination is made as to whethera bus error or timeout has occurred. If an error or timeout hasoccurred, then the program will proceed to set an unknown error flag andthe transmission will be terminated, as shown at steps 792 and 795. Ifnone of these instances has occurred, then the program will proceed tostep 789 to determine if the RDVAL flag has been set to indicate if thelast data byte has been successfully read. If it has been successfullyread, then this is an indication that the external device has notfinished sending data or that not enough address locations have beenallocated and an error flag will be set as shown at step 790 and thetransmission will be terminated at step 795. If the last data value hasbeen successfully read at step 789, then the process will continue tolook for the modified I² C bus master stop bit at step 786 until eitheran internal handshake timer (not shown) times out or an error occurs(step 788).

Read Block Routine

As mentioned above, the battery will return a calculated or measurementdata value to a specified address location as indicated by the readblock routine 800 as illustrated in FIG. 18. At step 802, adetermination is first made as to whether the data value to be writtento the host device is greater than two bytes long. If the data is longerthan two bytes, i.e., if count >2, then the address is pointed to atstep 805 and the program enters a loop indicated as steps 808, 812, and815 wherein each byte of data is sequentially written to the SMBus busto an address location of the requesting host device as indicated atstep 812. After each byte is sent, the count of the number of bytes isdecremented and the address location for the next byte to be written isincremented. Until count=0, indicating that the last byte of data hasbeen transmitted to the external device as shown at step 815, the loopwill continue and enter at step 808 to determine if the acknowledge bithas been sent by the external device indicating that the current databyte has been successfully transmitted. If the acknowledge bit has beenreceived after each byte transfer, the loop continues at step 812 untilthe last data byte is sent.

If the acknowledge bit has not been received, then an error may haveoccurred and the program proceeds to step 821 where a determination ismade as to whether a bus error, termination, or timeout has occurred. Ifnone of these instances has occurred, then the program will proceed tostep 808 to again determine if the data byte acknowledge bit has beenreceived. This process will continue until an internal handshake timer(not shown) times out wherein the process will continue at step 825where an unknown error flag is set and the transmission will beterminated. After it is determined that the last data byte has been sent(step 818) then a flag indicating that the last byte has been sent isset at step 818 of FIG. 18. In view of FIG. 18, it is understood that insome cases, no data is to be returned as shown at step 802, and thealgorithm will proceed directly to step 812 and bypass the receiptacknowledgment bit step 808.

Next, as indicated at step 822, a determination is made as to whetherthe stop bit flag has been received from the I² C bus master indicatingthe end of bus control due to the fact that the external device will notbe receiving any more data. If the stop bit is received the read blockis exited. If the stop bit has not been received, then an error may haveoccurred and the program proceeds to step 824 where a determination ismade as to whether a bus error or timeout has occurred. If none of theseinstances has occurred, then the program will proceed to step 822 toagain determine if the stop bit has been received. This process willcontinue until an internal handshake timer (not shown) times out whereinthe process will continue at step 825 where an unknown error flag is setand the transmission will be terminated.

Alarm Control

All of the alarm status flags heretofore mentioned indicate that thebattery has reached a certain state of charge (fully charged, emptydischarged) or a critical state (maximal temperature, beingovercharged). These events are encoded in the Al Status battery registerand the warning message AlarmWarning() is sent by battery to an externaldevice when the battery detects an alarm condition. In this event, thebattery becomes the bus master and alternately notifies the hostcomputer or battery charger of any critical and/or alarm conditions at arate of preferably once every five seconds, until the critical state iscorrected. The alarm condition may be broadcast to the host computer for10 seconds if alarm condition is such that the battery charger does notneed to be notified of an alarm condition, for e.g., the REMAINING CAPALARM warning message is not the broadcast to the charger device. Ifalarm conditions such as OVER CHARGED ALARM, TERMINATE CHARGE ALARM,DTEMP ALARM, OVER TEMP ALARM, and TERMINATE DISCHARGE ALARM exist, thenthe alarm is broadcast, alternating between the charger device and thehost device, in five (5) second intervals.

The modified SMBus protocol for communicating alarm or warning messagesare illustrated in the alarm control routine 152 as shown in detail inFIG. 19. This routine runs through all possible alarm conditions forpossible broadcast to a host device after a capacity calculation isperformed as shown in FIG. 3.

The first step, indicated as step 901 in FIG. 19 is to verify the statusof the remaining capacity. Specifically, a determination is made as towhether the AL REM CAP run value is greater than 0 and that theremaining capacity (less the uncertainty error) is less than the AL REMCAP value. If these conditions hold true, the REMAINING CAPACITY ALARMbit is set at step 904. If none of these conditions holds true, theREMAINING CAPACITY ALARM bit is cleared at step 906. Next, the C ratebased on the one minute rolling average current is calculated and theresidual capacity based on the C rate pd avg:=pd(C rate(I avg), T)! isaccessed from the look-up table of FIG. 22(a). Then, at step 910, adetermination is made as to whether the battery state is capacitydecreasing. If the battery capacity is decreasing, then a determinationis made at step 913 as to whether the AL REM TIME alarm threshold valueis greater than zero (0). If so, then the estimated remaining time atthe present discharge rate is calculated at step 915 by theAverageTimeToEmpty() command code. When the calculated remaining timefalls below the AL REM TIME threshold value, as determined at step 917,the program sets the REMAINING TIME ALARM bit as indicated at step 919and the program proceed at step 925 shown in FIG. 19. If, it isdetermined either that the battery state is not capacity decreasing(step 910), or, that the AL REM TIME is equal to zero (step 913), or,that the calculated remaining time falls below the AL REM TIME thresholdvalue (step 917), then the program clears the REMAINING TIME ALARM bitas indicated at step 921 and the program proceed at step 925 shown inFIG. 19. As shown at step 925, the upper byte of the Alarm statusregister is checked to determine if any alarm bits, e.g., alarm bitssuch as OVER CHARGED ALARM, TERMINATE CHARGE ALARM, DTEMP ALARM, OVERTEMP ALARM, TERMINATE DISCHARGE ALARM, REMAINING CAPACITY ALARM, and,REMAINING TIME ALARM have been set. If so, then a check of the alarmbroadcast flag "alarming" is made at step 927. If the upper byte of theAlarm status register indicates no alarm condition, i.e., no bits set,then the process will continue at step 926 and the alarming broadcastflag is cleared. Note, that upon initialization, the alarming broadcastflag is not set. However, as long as an alarm condition exists, thisflag will be set. Therefore, as shown at step 927, if the alarming flagis cleared, the process continues and the alarming flag is set at step930. Additionally, at step 930, the alarm broadcast timer is set tozero, and, the "alarm to host" flag is set indicating that the alarmwill be sent to a host external device and not a battery charger. Theprocess continues at step 933, where a determination is made as towhether the alarm broadcast timer has timed out (=0). Since thebroadcast timer has been set to zero at step 930 for this firstoperating cycle of the alarm condition, or, if the alarm broadcast timerhas timed out, then the process will continue at step 935. If the timerhas not timed out, then the alarm control process is exited. At step935, the address location for the alarm broadcast is set to the hostdevice, and the command code is set equal to the battery statusBatteryStatus()! function described above. This will initiate thetransfer of the particular alarm to the host device. A determination isthen made at step 937 as to whether the alarm to host flag is cleared(=0). During the first operating cycle of the alarm condition (step930), the alarm to host flag had been set (=1) so the algorithm skipsover steps 940 and 943 (discussed below) and performs the send messageroutine 945 which changes the function of the battery as having busmaster control so that the alarm message can be sent. Details of thesend message routine 945 will be explained in detail below. Afterwards,at step 947, the broadcast alarm timer is reset to its 10 second time (NALARM) and the alarm sent to host flag is toggled to the alarm sent tocharger flag.

After the message is initiated to broadcast an alarm warning message tothe host device at step 945 (by the send message routine), and, thealarm broadcast timer has been reset, then the process continues. Afterthe next capacity calculation (FIG. 3), if the alarm condition stillexists (i.e., the alarm bits are set) at step 925, the process iscontinued. However, for the next and subsequent operating cycles of thealarm condition, the alarming flag has already been set as determined(at step 927), so the alarm broadcast timer (initialized as 10 seconds)is decremented at step 931 until the timer has timed out or the alarmstatus has been changed. Thus, after the broadcast timer hasdecremented, the process continues at step 933, where a determination ismade as to whether the alarm broadcast timer has timed out (=0). If thebroadcast timer has not timed out, then the alarm control routine isexited and these set of steps will continue until the alarm broadcasttimer has timed out (step 933). Until the alarm message has beenbroadcast to the host device for preferably five (5) seconds, then steps935 and 937 will not be performed. When the broadcast timer has timedout, and, since the alarm to host flag has toggled (during the firstoperating cycle of the alarm condition), the condition at step 937 willbe true. Therefore, the address location for the alarm broadcast ischanged and set to the battery charger at step 940, and the program willproceed to step 943 where a determination is made as to whether theparticular alarm warning message is meant to be sent to the batterycharger for the next 10 seconds. If, the alarm condition is not meant tobe transmitted to the battery charger, then the send message routine(step 945) will be bypassed, and the broadcast timer will be reset atstep 947 and the alarm to host bit toggled so that the message will beretransmitted to the host device.

Charger Control

Whenever the BatteryMode() CHARGER MODE bit is set to zero, and thebattery detects the presence of a smart battery charger, the battery isable to communicate with the smart battery charger and will sendChargingCurrent() and ChargingVoltage() values to the smart batterycharger. The ChargingCurrent() function sets the maximum current that asmart battery charger may deliver to the battery and will return thedesired charging rate in mA. This allows the battery charger todynamically adjust its output current to match optimal rechargingrequirements. A maximum value of 0×FFFF means constant voltage chargingwith the output value of ChargingVoltage(). Results are broadcast withthe battery as active bus master under the conditions set forth in thecharger control routine 154 of FIGS. 3 and 20.

The first step 850 in FIG. 20 is to determine whether the battery is inthe system. If not, CAPACITY MODE and CHARGER MODE variables are clearedat step 853 and the routine is exited. If the battery is installed inthe system, a determination is made at step 855 as to whether thebattery was just inserted in the system. If the battery was justinserted, then the message timer is set to one (1), and the CAPACITYMODE and CHARGER MODE variables are cleared at step 857 and thealgorithm continues at step 859. If the battery has not just beeninserted (step 855), then the algorithm skips to step 859 where adetermination is made as to the state of the charger mode bit. If thebit is not cleared at step 859, then the routine is exited. If theCHARGER MODE bit is set at step 859 then the timer is decremented atstep 861. The next step at 863 is to determine whether the message timerhas timed out. If it has, then the message timer is reset at step 865and the charging current calculation is additionally made. If themessage timer has not timed out at step 863, then the routine is exited.The next step 866 is to determine whether the returned value of thecalculated charging current is zero. If the charging current valuereturned is zero, then the process proceeds at step 868. If the chargingcurrent is not zero, then the determination is made at step 867 as towhether the state is capacity increasing (CI). If the battery is in a CIstate, then the process proceeds at step 868. If the capacity isdecreasing, then the routine is exited.

At step 868, the address location for the charger broadcast is set tothe battery charger, and the command code is set equal to the commandcode ChargingCurrent(). Next, at step 870, the charging current commandmessage is sent to the battery charger by the send message routine(discussed below). Then, at step 872, the maximum value (hex FFFF) fedinto the ConstantVoltage() function which indicates that the chargerwill be a constant current charging device. This instruction isbroadcast to the charger via the send message routine at step 874. Afterthe charging current is broadcast, the routine is finally exited.

Send Message Routine

As indicated at step 945 in FIG. 19 and step 870 in FIG. 20, the sendmessage routine changes the function of the battery to have bus mastercontrol so that the alarm messages can be sent. FIG. 21 illustrates thesend message routine.

The first step 950 is to determine the data bus availability. If it isdetermined that the data bus is available, then the first piece of datato be sent is the slave address, i.e., the address of the external hostdevice or battery charger, as indicated at step 952. As soon as the databus is acquired, then two flags are set; the first flag is an internallygenerated flag that is set to indicate that the battery now has busmaster control (step 953), and, the second flag is the transmissiontermination flag that is cleared at step 954. The next step, asindicated at step 955, is a check as to whether the acknowledge bit hasbeen sent, i.e., whether the first byte of data (slave address) has beenreceived by the slave device. If the acknowledge bit has not been sent,then a check is made at step 958 to determine if the bus is busy. If thebus is now busy, then the program continues at step 960 of FIG. 21. Ifthe bus is not busy at step 958, then a determination is made as towhether a bus error or timeout flag has been generated at step 959. Ifan error or timeout has occurred, then the program will proceed to step973 where the transmission will be terminated and the routine exited. Ifan error or timeout condition does not exist, the routine will continueat step 955 until an acknowledge bit has been sent by the slaveindicating that the data has been received. If the acknowledge bit hasbeen received, then the current command code is transmitted at step 957.It should be understood that when the send message routine is invokedduring a critical alarm condition, then the command code word is set tothe battery address (see step 935, FIG. 19) and the slave will recognizethat only two bytes of data are to be sent. The next step, as indicatedat step 960, is a check as to whether the acknowledge bit has been sent,i.e., whether the command code (or battery address) has been received bythe slave device. If the acknowledge bit has not been received, then acheck is made at step 962 to determine whether a bus error or timeoutflag has been generated. If an error or timeout has occurred, then theprogram will proceed to step 973 where the transmission will beterminated and the routine exited. If an error or timeout condition doesnot exist, the routine will continue at step 960 until it isacknowledged that the command code (or battery address) has beenreceived. If the acknowledge bit has been received, then the first byteof data is transmitted to the specified address location (see step 935,FIG. 19) at step 965. The next step, as indicated at step 966, is acheck as to whether the acknowledge bit has been sent, i.e., whether thefirst byte of command code data has been received by the slave device.If the acknowledge bit has not been received, then a check is made atstep 967 to determine whether a bus error or timeout flag has beengenerated. If an error or timeout has occurred, then the program willproceed to step 973 where the transmission will be terminated and theroutine exited. If an error or timeout condition does not exist, theroutine will continue at step 966 until it is acknowledged that thefirst data byte has been received. If the acknowledge bit has beenreceived, then the second byte of data is transmitted to the nextaddress location at step 968. The next step, as indicated at step 969,is a check as to whether the acknowledge bit has been sent, i.e.,whether the second byte of command code data has been received by theslave device. If the acknowledge bit has not been received, then a checkis made at step 971 to determine whether a bus error or timeout flag hasbeen generated. If an error or timeout has occurred, then the programwill proceed to step 973 where the transmission will be terminated andthe routine exited. If an error or timeout condition does not exist, theroutine will continue at step 969 until it is acknowledged that thesecond data byte has been received. After the full message has beentransmitted by the battery to the slave device, the send message routineis exited.

LED Display

As shown in FIG. 2(a), the battery 10 of the instant invention providesmanually controlled four (4) segment light emitting diode (LED) displayindicating the relative state of charge of the battery (similar to afuel gauge) with respect to the full cap value. After the capacitycalculation, alarm control 152, and charger control 154 routines areperformed during each 500 msec period (operating cycle), the system willlook for a hardware trigger of the LED display. At any time, a user caninitiate the LED display by a switch 35 on the battery 10 as shown inFIG. 2(a). The control logic for generating the LED display is describedin detail (in view of steps 975 through 996 of FIG. 15) in co-pendingpatent application (USSN 08/318,004).

While the invention has been particularly shown and described withrespect to the preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention, which should be limited only by the scope of theappended claims.

We claim:
 1. A method of customizing a battery system for a specificapplication, the battery system comprising a rechargeable battery, meansto sense and to generate signals representing a plurality of batteryparameters, and an integrated circuit including a processor forperforming predefined calculations using digital values representingbattery voltage, battery temperature and battery current, the methodcomprising:forming the integrated circuit from a multitude of layers,said multitude of layers including upper and lower layers; forming arandom access memory area from the lower layers of the integratedcircuit, and storing a plurality of variable data values in said lowerlayers; and forming a read only memory area from the upper layers of theintegrated circuit, and storing a plurality of fixed data values in saidupper layers.
 2. A method according to claim 1, wherein the step offorming the integrated circuit includes the step of forming said upperlayers by using a metal mask.
 3. A method according to claim 1, whereinthe step of storing a plurality of fixed data values in said upperlayers includes the step of storing a unique battery identification codein said upper layers.
 4. A method according to claim 1, wherein the stepof forming a read only memory area from the upper layers includes thestep of storing a plurality of fixed algorithms in said upper layers. 5.A method according to claim 1, wherein the battery system is for acustomer having a need for a specific algorithm, and wherein the step offorming a read only memory area includes the step of storing saidspecific algorithm in said upper layers.
 6. A method according to claim1, wherein the step of forming the integrated circuit includes the stepsof:providing each of said upper layers with a matrix consisting of nrows and m columns, the rows and columns intersecting to form n ×mmatrix locations; and locating a respective one transistor at each oneof the matrix locations.
 7. A method according to claim 6, wherein eachof the transistors includes a source terminal and a drain terminal, andthe step of forming the integrated circuit further includes the stepsof:providing each of the upper layers with a plurality of common lineshaving a common electrical voltage level; directly connecting the sourceterminals of selected transistors in each of the upper layers to thedrain terminals of other transistors; and directly connecting both thesource and drain terminals of other selected transistors in each of theupper layers to one of the common lines.
 8. A method according to claim7, wherein the transistors in each of said upper layers consist of firstand second groups of transistors, and wherein the step of forming theintegrated circuit further includes the steps of:in each of said upperlayers, directly connecting the source terminals of the first group oftransistors to the drain terminals of others of the transistors, anddirectly connecting the source and drain terminals of the second groupof transistors to one of the common lines.
 9. A method according toclaim 7, wherein the step of directly connecting both the source anddrain terminals of said other selected transistors in each of the upperlayers to one of the common lines includes the step of directlyconnecting the source and drain terminals of each of said other selectedtransistors to the same one of the common lines.
 10. A method accordingto claim 1 wherein:the means to sense and to generate signalsrepresenting battery voltage, battery temperature and battery currentincludes sensing means for sensing, and generating analog signalsrepresenting battery voltage, battery temperature and battery current;the integrated circuit further includes an analog-to-digital converterfor receiving said analog signals and converting said analog signals todigital values representing battery voltage, battery temperature andbattery current; and the processor is connected to the analog-to-digitalconverter for receiving the digital values therefrom.